Document No. PD0192 REV 4
Automotive Service Solutions QMS
Threads
Table of Contents
General Thread Symbols and Definitions ............................................................................................................................... 2
THREAD CLASS AND TAP SIZE .......................................................................................................................................... 3
Standard System of Tap Marking ........................................................................................................................................... 4
Dryseal American Standard, Internal...................................................................................................................................... 5
Dryseal American Standard, External .................................................................................................................................... 6
British Standard Pipe, Internal ................................................................................................................................................ 7
British Standard Pipe, External............................................................................................................................................... 8
Inch Thread Size Limits .......................................................................................................................................................... 9
Inch Thread - Tap Drill Size - Thread Pitch Diameter...........................................................................................................11
Inch Thread Form Tap Drill Selector Chart........................................................................................................................... 12
METRIC THREAD -- COARSE PITCH (1mm - 68mm) .......................................................................................................13
METRIC THREAD -- FINE PITCH (1 mm - 18 mm) ............................................................................................................14
METRIC THREAD -- FINE PITCH (20 mm – 40 mm) .........................................................................................................16
Formula for cutting Tap/Drill Sizes (Metric) .......................................................................................................................... 17
Metric Form Tap - Drill Selector Chart .................................................................................................................................. 17
Blank Diameters For Straight Rolled Threads ......................................................................................................................18
Bar or Turn Sizes for Rolled 6g Metric External Thread .......................................................................................................19
Threaded Rod....................................................................................................................................................................... 20
General Purpose Acme Threads – single start.....................................................................................................................21
Print Date: May 31, 2013
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Document No. PD0192 REV 4
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General Thread Symbols and Definitions
Taps, dies, and other threading tools will be marked with the nominal size, number of threads per inch, and the
proper symbol to identify the thread form. These symbols are in agreement with the Proposed A.S.A. B 1.8
Standard on Nomenclature, Definitions and Letter Symbols for Screw Threads
Symbols used for American National Threads:
NC
Amer. Nat. Coarse-Thread Series
NF
Amer. Nat. Fine Thread Series
NEF
Amer. Nat. Extra Fine Thread Series
NS
Special Threads of Amer. Nat. Form
NPT
Amer. Standard Taper Pipe Thread **
NPTF
Amer. Standard Taper Pipe Thread (Dryseal) ***
NPS
Amer. Standard Straight Pipe Thread
PTF
Amer. Standard Dryseal Pipe Thread -- SAE Short
NPSC
Amer. Standard Straight Pipe Thread for couplings
NPSF
Amer. Standard Internal Straight Pipe Thread (Dryseal)
NPSL
Amer. Stand. Straight Pipe Thread for Locknut pipe threads.
NPSM
Amer. Stand. Straight Pipe Thread for Mechanical Joints
ACME
Acme Threads -- (Centralizing “C” and General purpose “G”)
STUB
Acme Stub Acme Threads
Symbols used for American Standard Unified Threads:
UNC
Unified Coarse thread series
UNF
Unified Fine thread series
UNEF
Unified Extra Fine thread series
UN
Unified constant pitch series
UNS
Unified Special thread series
UNJ
Unified Inch Screw thread (Root radius thread form used in Aerospace industry)
British Threads symbols:
BSPT
British Standard Pipe Taper
BSPP
British Standard for Parallel Pipe
Thread Classifications – Inch
1A, 2A, and 3A apply to external threads. 1B, 2B, and 3B apply to internal threads.
The higher number being the closest fit. Unless otherwise specified, class 2 will apply.
Thread Classifications – Metric
8g, 6g, and 4h apply to external threads. 7H, 6H, and 5H apply to internal threads.
The lower number being the closest fit. Unless otherwise specified, class 6 will apply.
Thread Designation – The standard method is to specify the nominal size, the pitch (in threads per inch or
mm), followed by the thread class.
Example: .250 - 20 UNC - 2A
or
M10 X 1.5 - 6g
Unless otherwise specified, all threads are Right-Hand. A Left-Hand thread is designated as “LH”.
Example: .375 - 24 UNF - 2B - LH
** It is acceptable to use NPTF threads where NPT threads are specified.
*** NPTF (Standard Taper Pipe Thread Dryseal) is recommended for all new designs (since 1972).
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Document No. PD0192 REV 4
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THREAD CLASS AND TAP SIZE
There is a direct relationship between the size of a tap and the size of the thread that it cuts. Size refers to
pitch diameter and its relationship to the class of fit required. If two threaded parts are assembled, the
looseness or tightness of the fit is determined by contact on the flanks of the threads only. This contact is
controlled by the pitch diameters of each part.
CLASSES OF THREAD: (i.e. 2B, 3B, etc. B signifies internal thread, A external)
When threaded parts are mated, the two parts must assemble with a degree of tightness dictated by the use of
the fastener. In addition, the internal thread must be large enough to allow the external thread to enter it for the
required length of engagement. A system of thread classes, each representing a comparative degree of
tightness, has been established and universally adopted, to provide manufacturers and users of threaded
products with a common language of specification. The thread classes designate minimum and maximum pitch
diameters for internal and external threads. It is important to remember that classes of thread actually
represents manufacturing tolerances. The closer the tolerance required, the higher the cost involved in
producing the parts. Therefore, designers and engineers should always try to select the class of thread with the
widest permissible tolerance.
TAP SIZE:
Due to material variability and machining conditions, taps rarely cut their own size. The thread size produced is
usually larger, but can be smaller due to shrinkage. Tap manufacturers realized that to tap a specified class of
thread, several different ground thread tap limits would be required. These limits represent small, defined
variations in tap size. A numbering system (see next page for tap marking) was developed to designate each
series of limits, but these limit numbers are not to be confused with the classes of threads.
On the chart below, an example of the relationship of Class of Fit to various tap limit sizes is shown. Using a
1/4"-20 UNC thread size, it is obvious that an H5 limit (+.0025" over basic pitch diameter) can be used to cut
the tightest class of thread in most machining situations, as can the H1 limit (+.0005" over basic P.D.).
However, tool wear would force the discarding of the H1 tap long before the H5 would be worn to an undersize
condition. The rule is obvious: always select the largest "H" limit possible to achieve proper class of fit, and
maximum tool life.
Comparison of Class of Fit to Pitch Diameter Limits
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Document No. PD0192 REV 4
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Standard System of Tap Marking
Taps, dies and other types of threading tools are marked according to the Standard System of Marking Ground
Thread Taps. Tools are marked with the nominal size, number of threads per inch (pitch), and the appropriate
thread form symbol and pitch diameter symbol.
Pitch Diameter Limit Symbols
All standard ground thread taps are marked with the letter "G" to designate Ground Thread. The letter “H” to
designate above basic; or the letter “L” to designate below basic will follow the letter G. The number following
H or L signifies the number of .0005" steps above or below the basic pitch diameter.
For instance, the tap pictured above is a 3/8" dia. tap with 20 threads per inch (pitch), and has an NS thread
form. The tap is made from High Speed Steel, and the GH-3 pitch diameter limit symbol indicates a Ground
Thread tap with pitch diameter limits .0010 to .0015 over basic. ( 3 X .0005 = .0015. Subtract .0005 for the
tolerance.)
Pitch Diameter Limits for taps to 1" diameter inclusive are ground to a .0005" tolerance.
L1 = Basic to Basic minus .0005
H1 = Basic to Basic plus .0005
H2 = Basic plus .0005 to Basic plus .0010
H3 = Basic plus .0010 to Basic plus .0015
H4 = Basic plus .0015 to Basic plus .0020
H5 = Basic plus .0020 to Basic plus .0025
H6 = Basic plus .0025 to Basic plus .0030
Pitch Diameter Limits for taps between 1.000 and 1.500” diameter are ground to a .001" tolerance.
H4 = Basic plus .001" to Basic plus .002"
H6 = Basic plus .002” to Basic plus .003
For H numbers not listed, simply multiply the number times .0005 and subtract 1step for that size range.
Example, H12 for a 1-1/4 tap would be 12 X .0005 for the high limit, minus .001 for the low limit for a tolerance
of .006/.005 above basic pitch diameter.
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Document No. PD0192 REV 4
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Dryseal American Standard, Internal
Pipe Threads - Internal N.P.T.F.
TAP DRILL SIZES FOR PIPE TAPS WITHOUT REAMING PRIOR TO TAPPING
Tap Drill Size
Std.*
Std.**
(Class A)
Nom. Size
Min.
Min.
Inches
Drill
Drill
Countersink
(N.P.T.F)
Depth
Depth
Dia. X 90 INCL
(Thru Hole)
(Blind Hole)
Drill
Decimal
.062 -27
.125 -27
.250 -18
.375 -18
.500 -14
.750 -14
1.000 - 11-1/2
1.250 - 11-1/2
1.500 - 11-1/2
2.000 - 11-1/2
2.500 - 8
3.000 - 8
D
8.5mm
7/16
14.5mm
45/64
59/64
1-5/32
1-1/2
1- 47/64
2 -7/32
2 - 41/64
3 -17/64
.246
.3346
.4375
.5709
.7031
.9219
1.156
1.500
1.734
2.219
2.641
3.266
9/16
9/16
13/16
13/16
1-1/16
1-1/16
1-1/4
1 5/16
1 5/16
1 5/16
1 27/32
1 29/32
21/32
3/4
1”
1”
1-3/16
1-1/4
1-3/8
1-1/2
1-1/2
1-1/2
1-61/64
2 -1/32
.330
.420
.550
.690
.850
1.060
1.340
1.680
1.920
2.390
2.890
3.520
+.020/-.000
+.020/-.000
+.020/-.000
+.020/-.000
+.020/-.000
+.030/-.000
+.030/-.000
+.030/-.000
+.030/-.000
+.040/-.000
+.040/-.000
+.040/-.000
Pipe Threads - Internal P.T.F. - SAE Short
Tap Drill Sizes For Pipe Taps Without Reaming Prior To Tapping
Nom. Size
In Inches
Tap Drill Size
Class “A”
P.T.F., SAE
Short
Drill
Decimal
.125 -27
.250 -18
.375 -18
8.5.mm
7/16
14.5mm
(.3346)
(.4375)
(.5709)
Std. Min.*
Drill
Depth
(Through
Hole)
Std. Min.**
Drill
Depth
(Blind Hole)
.437
.656
.656
.625
.843
.843
Countersink
Dia. x 90 Incl.
.420
.550
.690
+.020/-.000
+.020/-.000
+.020/-.000
NOTE: Drawings will show thread size in decimal form effective 1/1/99.
EXAMPLE:
Print Date: May 31, 2013
.250-18 NPTF.
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Document No. PD0192 REV 4
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Dryseal American Standard, External
Pipe Threads - External N.P.T.F.
D1
D2
+.003
--.000
O.D. Of
Fitting
O.D.
Of
Pipe
+ .003
--.000
.062 - 27
.315
.3125
.125 - 27
.407
.250 - 18
Size
(NPTF)
B
H
TL
Min.
R.
Max.
L2
L1
Imp
Thread
.301
.230 +.000/-.020
.125
.375
.030
.261
.160
.129
.405
.393
.320 +.000/-.020
.187
.375
.030
.264
.161
.129
.546
.540
.523
.420 +.000/-.020
.281
.562
.060
.402
.228
.193
.375 - 18
.681
.675
.658
.550 +.000/-.020
.406
.562
.060
.408
.240
.193
.500 - 14
.850
.840
.820
.680 +.000/-.020
.562
.750
.080
.534
.320
.248
.750 - 14
1.060
1.050
1.029
.890 +.000/-.020
.718
.750
.080
.546
.339
.248
1.000 - 11-1/2
1.327
1.315
1.289
1.120 +.000/-.030
.938
.937
.090
.683
.400
.302
1.250 - 11-1/2
1.627
1.660
1.633
1.460 +.000/-.030
1.250
.968
.090
.707
.420
.302
1.500 - 11-1/2
1.912
1.900
1.872
1.700 +.000/-.030
1.468
1.00
.090
.724
.420
.302
2.000 - 11-1/2
2.387
2.375
2.345
2.170 +.000/-.030
1.940
1.03
.090
.756
.436
.302
2.500 - 8
2.893
2.875
2.829
2.590 +.000/-.030
2.310
1.520
.120
1.138
.682
.434
3.000 - 8
3.518
3.500
3.450
3.210 +.000/-.030
2.910
1.580
.120
1.200
.766
.434
Print Date: May 31, 2013
A
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Document No. PD0192 REV 4
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British Standard Pipe, Internal
Pipe Threads - Internal - B.S.P.T (tapered) and B.S.P.P (straight)
RECOMMENDED TAP DRILL SIZES
B.S.P.P.
Tap Drill Size
(Class A)
B.S.P.T
Tap Drill Size
(Class A)
Size
Std.*
Min.
Drill
Depth
(Thru
Hole)
Std.**
Min.
Drill
Depth
(Blind
Hole)
Countersink
Dia. X 90 INCL
.062 -28
.125 -28
.250 -19
.375 -19
.500 -14
.750 -14
Drill
6.4 mm
8.4 mm
11.2 mm
14.75 mm
18.25 mm
23.75 mm
Decimal
.2519
.3307
.4409
.5807
.7185
.9350
Drill
N/A
8.7 mm
11.6 mm
15 mm
19 mm
24.5 mm
Decimal
N/A
.340
.460
.590
.750
.960
9/16
9/16
13/16
13/16
1-1/16
1-1/16
21/32
3/4
1”
1”
1-3/16
1-1/4
.330
.420
.550
.690
.850
1.070
+.020/-.000
+.020/-.000
+.020/-.000
+.020/-.000
+.020/-.000
+.030/-.000
1.000 - 11
30 mm
1.1811
30.5 mm
1.200
1-1/4
1-3/8
1.340
+.030/-.000
1.250 - 11
38.5 mm
1.5157
39.5 mm
1.560
1 5/16
1-1/2
1.680
+.030/-.000
1.500 - 11
44.5 mm
1.7519
45 mm
1.770
1 5/16
1-1/2
1.920
+.030/-.000
2.000 - 11
56 mm
2.2047
57 mm
2.240
1 5/16
1-1/2
2.380
+.040/-.000
2.500 - 11
71 mm
2.7952
72.5 mm
2.850
1 27/32
1-61/64
2.990
+.040/-.000
3.000 - 11
85.5 mm
3.3661
85.5 mm
3.370
1 29/32
2 -1/32
3.490
+.040/-.000
NOTE: Drawings will show thread size in decimal form effective 1/1/99.
EXAMPLE:
Print Date: May 31, 2013
.250-19 BSPT.
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Document No. PD0192 REV 4
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British Standard Pipe, External
Pipe Threads – External – B.S.P.T. and B.S.P.P.
Size
(NPTF)
D1
+.005
--.000
Major O.D.
A
B
Pitch Dia.
for BSPP
TL
Min.
R.
Max.
.062 - 28
.305
.290
.230 +.000/-.020
N/A
.375
.030
.125 - 28
.383
.364
.320 +.000/-.020
.3601
.375
.030
.250 - 19
.518
.492
.420 +.000/-.020
.4843
.562
.060
.375 - 19
.656
.623
.550 +.000/-.020
.6222
.562
.060
.500 - 14
.825
.784
.680 +.000/-.020
.7792
.750
.080
.750 - 14
1.041
.989
.890 +.000/-.020
.9952
.750
.080
1.000 - 11
1.309
1.244
1.120 +.000/-.030
1.2508
.937
.090
1.250 - 11
1.650
1.568
1.460 +.000/-.030
1.5918
.968
.090
1.500 - 11
1.882
1.788
1.700 +.000/-.030
1.8238
1.000
.090
2.000 - 11
2.347
2.230
2.170 +.000/-.030
2.2888
1.030
.090
2.500 - 11
2.960
2.812
2.590 +.000/-.030
2.9018
1.520
.120
3.000 - 11
3.460
3.287
3.210 +.000/-.030
3.4018
1.580
.120
Note: Dim A is approx. 95% of D1
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Document No. PD0192 REV 4
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Inch Thread Size Limits
Limits of Size for Standard Series - Unified Screw Threads
External
Normal
Size
and
Threads
Per
Inch.
10-24
Major Dia.
Internal
Pitch Dia.
Minor Dia.
Pitch Dia.
Series
Designation
UNC
.250 -20
UNC
.250 -28
UNF
.313-18
UNC
.313 -24
UNF
.375 -16
UNC
.375 -24
UNF
.438 -14
UNC
.438 -20
UNF
.500 -13
UNC
.500 -20
UNF
.563 -12
UNC
.563 -18
UNF
.563 -20
UN
Print Date: May 31, 2013
Class
Max.
Min.
Max.
Min.
Minor
Dia.
Class
2A
3A
2A
3A
2A
3A
2A
3A
2A
3A
2A
3A
2A
3A
2A
3A
2A
3A
2A
3A
2A
3A
2A
3A
2A
3A
2A
3A
.1890
.1900
.2489
.2500
.2490
.2500
.3113
.3125
.3114
.3125
.3737
.3750
.3739
.3750
.4361
.4375
.4362
.4375
.4985
.5000
.4987
.5000
.5609
.5625
.5611
.5625
.5612
.5625
.1818
.1828
.2408
.2419
.2425
.2435
.3026
.3038
.3042
.3053
.3643
.3656
.3667
.3678
.4258
.4272
.4281
.4294
.4876
.4891
.4906
.4919
.5495
.5511
.5524
.5538
.5531
.5544
.1619
.1629
.2164
.2175
.2258
.2268
.2752
.2764
.2843
.2854
.3331
.3344
.3468
.3479
.3897
.3911
.4037
.4050
.4485
.4500
.4662
.4675
.5068
.5084
.5250
.5264
.5287
.5300
.1586
.1604
.2127
.2147
.2225
.2243
.3712
.2734
.2806
.2827
.3287
.3311
.3430
.3450
.3850
.3876
.3995
.4019
.4435
.4463
.4619
.4643
.5016
.5045
.5205
.5230
.5245
.5268
.1379
.1389
.1876
.1887
.2052
.2062
.2431
.2443
.2603
.2614
.2970
.2983
.3228
.3239
.3485
.3499
.3749
.3762
.4041
.4056
.4374
.4387
.4587
.4603
.4929
.4943
.4999
.5012
2B
3B
2B
3B
2B
3B
2B
3B
2B
3B
2B
3B
2B
3B
2B
3B
2B
3B
2B
3B
2B
3B
2B
3B
2B
3B
2B
3B
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Min.
Max.
Min.
Max.
Major
Dia.
Min.
.145
.1450
.196
.1960
.211
.2110
.252
.250
.267
.2670
.307
.370
.330
.3300
.360
.3600
.383
.3830
.417
.4170
.446
.4460
.472
.4720
.502
.5020
.508
.5080
.156
.1555
.207
.2067
.220
.2190
.265
.2630
.277
.2754
.321
.3182
.340
.3372
.376
.3717
.395
.3916
.434
.4284
.457
.4537
.490
.4843
.515
.5106
.520
.5162
.1629
.1629
.2175
.2175
.2268
.2268
.2764
.2764
.2854
.2854
.3344
.3344
.3479
.3479
.3911
.3911
.4050
.4050
.4500
.4500
.4675
.4675
.5084
.5084
.5264
.5264
.5300
.5300
.1672
.1661
.2223
.2211
.2311
.2300
.2817
.2803
.2902
.2890
.3401
.3387
.3528
.3516
.3972
.3957
.4104
.4091
.4565
.4548
.4731
.4717
.5152
.5132
.5323
.5308
.5355
.5341
.1900
.1900
.2500
.2500
.2500
.2500
.3125
.3125
.3125
.3125
.3750
.3750
.3750
.3750
.4375
.4375
.4375
.4375
.5000
.5000
.5000
.5000
.5625
.5625
.5625
.5625
.5625
.5625
Page 9 of 21
Document No. PD0192 REV 4
Automotive Service Solutions QMS
Inch Thread Size Limits (continued)
Limits of Size for Standard Series - Unified Screw Threads
External

Normal
Size and
Threads
Per Inch.
.625 -11
Series
Designation
UNC
Major Dia.
.625 -18
UNF
.688 -18
UNS
.750 -10
UNC
.750 -16
UNF
.813 -16
UN
.875 - 9
UNC
.875 -14
UNF
1.000 -8
UNC
1.000 -12
UNF
1.000 -14
UNS
1.250 -7
UNC
1.250 12
UNF
1.500 -12
UNF
Class
2A
3A
2A
3A
2A
3A
2A
3A
2A
3A
2A
3A
2A
3A
2A
3A
2A
3A
2A
3A
2A
3A
2A
3A
2A
3A
2A
3A
Max.
.6234
.6250
.6236
.6250
.6861
.6875
.7482
.7500
.7485
.7500
.8110
.8125
.8731
.8750
.8734
.8750
.9980
1.000
.9982
1.000
.9983
1.000
1.2478
1.2500
1.2482
1.2500
1.4981
1.5000
Min.
.6113
.6129
.6149
.6163
.6774
.6788
.7353
.7371
.7391
.7106
.8016
.8031
.8592
.8611
.8631
.8647
.9800
.9850
.9868
.9886
.9880
.9897
1.2314
1.2336
1.2368
1.2386
1.4867
1.4886
Internal
Pitch Dia.
Max.
.5644
.5660
.5875
.5889
.6500
.6514
.6832
.6850
.7079
.7094
.7704
.7719
.8009
.8028
.8270
.8286
.9168
.9188
.9441
.9459
.9519
.9536
1.1550
1.1572
1.1941
1.1959
1.4440
1.4459
Min.
.5589
.5619
.5828
.5854
.6455
.6479
.6773
.6806
.7029
.7056
.7655
.7683
.7946
.7981
.8216
.8245
.9100
.9137
.9382
.9415
.9463
.9494
1.1476
1.1517
1.1879
1.1913
1.4376
1.4411
Minor Dia.
Minor
Dia.
.5119
.5135
.5554
.5568
.6179
.6193
.6255
.6273
.6718
.6733
.7348
.7358
.7368
.7387
.7858
.7874
.8446
.8466
.8960
.8978
.9107
.9124
1.0725
1.0747
1.1460
1.1478
1.3959
1.3978
Class
2B
3B
2B
3B
2B
3B
2B
3B
2B
3B
2B
3B
2B
3B
2B
3B
2B
3B
2B
3B
2B
3B
2B
3B
2B
3B
2B
3B
Min.
.527
.5270
.565
.5650
.627
.6270
.642
.6420
.682
.6820
.745
.7450
.755
.7550
.798
.7980
.865
.8650
.910
.9100
.923
.9230
1.095
1.095
1.160
1.1600
1.410
1.4100
Max.
.546
.5391
.578
.5730
.641
.6355
.663
.6545
.696
.6908
.759
.7533
.778
.7681
.814
.8068
.890
.8797
.928
.9198
.938
.9315
1.123
1.1125
1.178
1.1698
1.428
1.4198
Pitch Dia.
Min.
.5660
.5660
.5889
.5889
.6514
.6514
.6850
.6850
.7094
.7094
.7719
.7719
.8028
.8028
.8286
.8286
.9188
.9188
.9459
.9459
.9536
.9536
1.1572
1.1572
1.1959
1.1959
1.4459
1.4459
Max.
.5732
.5714
.5949
.5934
.6574
.6559
.6927
.6907
.7159
.7143
.7782
.7766
.8110
.8089
.8356
.8339
.9276
.9254
.9535
.9516
.9609
.9590
1.1668
1.1644
1.2039
1.2019
1.4542
1.4522
Revised Minor Diameter Limits of Class 2B are American Standard and have been submitted for consideration as Unified Standards.
Print Date: May 31, 2013
Automotive Service Solutions Confidential
QMS electronic document is the controlled copy
Page 10 of 21
Major
Dia.
Min.
.6250
.6250
.6250
.6250
.6875
.6875
.7500
.7500
.7500
.7500
.8125
.8125
.8750
.8750
.8750
.8750
1.000
1.000
1.000
1.000
1.000
1.000
1.250
1.250
1.250
1.250
1.500
1.500
Document No. PD0192 REV 4
Automotive Service Solutions QMS
Inch Thread - Tap Drill Size - Thread Pitch Diameter
Thread
Size
Int. Thread
Drill Size
Ext. Thread
Maj. Dia.
Ext. Thread
Pitch Dia.
Int. Thread
Pitch Dia.
4 - 40 UNC
5 - 40 UNC
6 - 32 UNC
43 - .089
38 - .1015
7/64 - .1094
.1112 - .1061
.1191 - .1242
.1312 - .1372
.0925 - .0950
.1054 - .1080
.1141 - .1169
.0958 - .0991
.1088 - .1121
.1177 - .1214
8 - 32 UNC
10-24 UNC-2
10 - 32 UNF
.250 - 20 UNC - 2
.250 - 28 UNF - 2
29 - .136
No. 24 -.152
20 - .161
No. 5 - .206
7/32 - .219
.1571 - .1631
.189 -.182
.1831 - .1891
.248 - .241
.249 - .234
.1399 - .1428
.1619 - .1586
.1658 - .1688
.2164 - .2127
.2258 - .2225
.1437 - .1475
.1629 - .1672
.1697 - .1736
.2175 - .2223
.2268 - .2311
.313 - 18 UNC - 2
.313 - 24 UNF - 2
.375 - 16 UNC - 2
.375 - 24 UNF -2
.438 - 14 UNC -2
.438 - 20 UNF -2
.500 - 13 UNC -2
.500 - 18 UNS
.500 - 20 UNF -2
.563 - 12 UNC - 2
.563 - 18 UNF -2
Let. G - .261
Let. J - .277
Let. O - .316
Let. R - .339
3/8 - .375
25/64 - .391
7/16 - .438
7/16 - .441
29/64 - .453
31/64 - .484
1/2 - .500
.311 - .303
.311 - .305
.373 - .365
.373 - .367
.436 - .426
.436 - .429
.498 - .488
.498 - .490
.498 - .491
.560 - .550
.561 - .553
.2752 - .2712
.2843 - .2806
.3331 - .3287
.3468 - .3430
.3897 - .3850
.4037 - .3995
.4485 - .4435
.4626 - .4582
.4662 - .4619
.5068 - .5016
.5250 - .52056
.2764 - .2817
.2854 - .2902
.3344 - .3401
.3479 - .3528
.3911 - .3972
.4050 - .4104
.4500 - .4565
.4639 - .4697
.4675 - .4731
.5084 - .5152
.5264 - .5323
.563 - 20 UN - 2
33/64 - 5.16
.561 - .554
.5287 - .5245
.5300 - .5355
.625 - 11 UNC - 2
35/64 - .547
.623 - .612
.5644 - .5589
.5660 - .5732
.625 - 18 UNF - 2
37/64 - .578
.623 - .615
.5875 - .5828
.5889 - .5949
5/8- .625
41/64 - .641
21/32 - .656
11/16 - .688
3/4 - .750
25/32 - .781
13/16 - .812
7/8 - .875
59/64 - .922
15/16 - .938
1 7/64 - 1.109
1 11/64 - 1.172
1 27/64 - 1.422
1 17/32 - 1.531
.686 - .677
.686 - .678
.748 - .736
.748 - .740
.811 - .802
.873 - .860
.873 - .864
.998 - .983
.998 - .987
.998 - .988
1.248 - 1.232
1.248 - 1.237
1.498 - 1.487
1.622 - 1.605
.6455 - .6407
.6500 - .6453
.6832 - .6773
.7079 - .7029
.7704 - .7655
.8009 - .7946
.8270 - .8216
.9168 - .9100
.9441 - .9382
.9519 - .9463
1.1550 - 1.1476
1.1941 - 1.1879
1.4440 - 1.4376
1.5044 - 1.4959
.6469 - .6531
.6514 - .6574
.6850 - .6927
.7094 - .7159
.7719 - .7782
.8028 - .8110
.8286 - .8356
.9188 - .9276
.9459 - .9535
.9536 - .9609
1.1572 - 1.1668
1.1959 - 1.2039
1.4459 - 1.4542
1.5069 - 1.5176
.688 - 16 UNF - 2
.688 - 18 UN - 2
.750 - 10 UNC - 2
.750 - 16 UNF - 2
.813 - 16 UN - 2
.875 - 9 UNC - 2
.875 - 14 UNF - 2
1.000 - 8 UNC - 2
1.000 - 12 UNF - 2
1.000 - 14 UNS - 2
1.250 - 7 UNC - 2
1.250 - 12 UNF - 2
1.500 - 12 UNF - 2
1.625 - 12 UNS - 2
Formula for Tap/Drill Sizes (Inch)
Drilled Hole Size (in.) = Basic Major Dia. of Thread (in.) - (.013 X % of Thread) divided by the threads per Inch.
Example: .250-20 tap and you want 75% threads. Tap drill size would be .250 minus (.013 X 75) divided by 20.
.013 X 75 = 975, divided by 20 = .04875. Subtract that from .250 = .201, therefore a .201 diameter tap drill will give
you 75% threads.
NOTE: 60 – 80% of full thread is recommended.
Unless otherwise noted, specified drill size and tolerance, determines internal thread minor diameter. This
takes precedence over standard minor diameter size and tolerance for the specified thread class.
Print Date: May 31, 2013
Automotive Service Solutions Confidential
QMS electronic document is the controlled copy
Page 11 of 21
Document No. PD0192 REV 4
Automotive Service Solutions QMS
Inch Thread Form Tap Drill Selector Chart
Normal
Thread
Size
0
1
1
2
2
3
3
4
4
5
5
6
6
8
8
10
10
12
12
.250
.250
.313
.313
.375
.375
.438
.438
.500
.500
.563
.563
.625
.625
.750
.750
Notes:
Threads
Per Inch
NC
UNC
64
56
48
40
40
32
32
24
24
20
18
16
14
13
12
11
10
-
NF
UNF
80
72
64
56
48
44
40
36
32
28
28
24
24
20
20
18
18
16
Minimum
Hole
Maximum
Hole
Diameter
Diameter
.053
.064
.065
.76
.077
.087
.089
.098
.100
.111
.112
.120
.123
.146
.148
.166
.172
.192
.195
.221
.229
.280
.288
.339
.351
.396
.409
.456
.471
.514
.530
.573
.584
.692
.714
.055
.066
.067
.079
.080
.091
.092
.102
.104
.115
.116
.125
.127
.151
.152
.173
.177
.199
.201
.229
.235
.289
.295
.349
.358
.408
.417
.469
.479
.528
.539
.587
.593
.709
.724
Maximum
Minor
Diameter
After
Tapping
.050
.061
.062
.072
.074
.083
.085
.093
.096
.106
.107
.114
.119
.140
.142
.157
.165
.183
.188
.211
.224
.269
.283
.326
.345
.381
.398
.444
.461
.497
.524
.555
.602
.672
.701
 Recommended
Drill Diameter
Fraction, No.,
or Letter
MM
1.35
52
1.65
48
1.95
2.20
43
40
38
34
33
31
1/8
26
25
19
17
4.90
9
5.75
5.90
9/32
L
R
9.00
X
Z
11.60
12.00
33/64
13.50
37/64
.586
45/64
23/32
15.00
1. May vary due to material density.
2. The maximum minor diameter after tapping must be satisfied.
If the drawing specifies the “Drill Size For Specials” form taps cannot be substituted without consulting Design
Engineering for a print change.
Print Date: May 31, 2013
Automotive Service Solutions Confidential
QMS electronic document is the controlled copy
Page 12 of 21
Document No. PD0192 REV 4
Automotive Service Solutions QMS
METRIC THREAD -- COARSE PITCH (1mm - 68mm)
Nominal
Pitch
Size
mm
1
1.1
1.2
1.4
1.6
1.8
2
2.2
2.5
3
3.5
4
4.5
5
6
7
8
9
10
11
12
14
16
18
20
22
24
27
30
33
36
39
42
45
48
52
56
60
64
68
mm
0.25
0.25
0.25
0.3
0.35
0.35
0.4
0.45
0.45
0.5
0.6
0.7
0.75
0.8
1
1
1.25
1.25
1.5
1.5
1.75
2
2
2.5
2.5
2.5
3
3
3.5
3.5
4
4
4.5
4.5
5
5
5.5
5.5
6
6
Major
Minor Dia Minor Dia Minor Dia Minor Dia
Tap
Tap
Diameter Diameter Diameter Male Thd Male Thd Fem Thd Fem Thd
Inch
mm
Inch
mm
Inch
mm
Inch
0.039
0.838
0.0330
0.693
0.0273
0.729
0.0287
0.043
0.938
0.0369
0.793
0.0312
0.829
0.0326
0.047
1.038
0.0409
0.893
0.0352
0.929
0.0366
0.055
1.205
0.0474
1.032
0.0406
1.075
0.0423
0.063
1.373
0.0541
1.171
0.0461
1.221
0.0481
0.071
1.573
0.0619
1.371
0.0540
1.421
0.0559
0.079
1.74
0.0685
1.509
0.0594
1.567
0.0617
0.087
1.908
0.0751
1.648
0.0649
1.713
0.0674
0.098
2.208
0.0869
1.948
0.0767
2.013
0.0793
0.118
2.675
0.1053
2.387
0.0940
2.459
0.0968
0.138
3.11
0.1224
2.764
0.1088
2.85
0.1122
0.157
3.545
0.1396
3.141
0.1237
3.242
0.1276
0.177
4.013
0.1580
3.58
0.1409
3.688
0.1452
0.197
4.48
0.1764
4.019
0.1582
4.134
0.1628
0.236
5.35
0.2106
4.773
0.1879
4.917
0.1936
0.276
6.35
0.2500
5.773
0.2273
5.917
0.2330
0.315
7.188
0.2830
6.466
0.2546
6.647
0.2617
0.354
8.188
0.3224
7.466
0.2939
7.647
0.3011
0.394
9.026
0.3554
8.16
0.3213
8.376
0.3298
0.433
10.026
0.3947
9.16
0.3606
9.376
0.3691
0.472
10.863
0.4277
9.853
0.3879
10.106
0.3979
0.551
12.701
0.5000
11.546
0.4546
11.835
0.4659
0.630
14.701
0.5788
13.546
0.5333
13.835
0.5447
0.709
16.376
0.6447
14.933
0.5879
15.394
0.6061
0.787
18.376
0.7235
16.933
0.6667
17.294
0.6809
0.866
20.376
0.8022
18.933
0.7454
19.294
0.7596
0.945
22.051
0.8681
20.319
0.8000
20.752
0.8170
1.063
25.051
0.9863
23.319
0.9181
23.752
0.9351
1.181
27.727
1.0916
25.706
1.0120
26.211
1.0319
1.299
30.727
1.2097
28.706
1.1302
29.211
1.1500
1.417
33.402
1.3150
31.093
1.2241
31.67
1.2469
1.535
36.402
1.4331
34.093
1.3422
34.67
1.3650
1.654
39.077
1.5385
36.479
1.4362
37.129
1.4618
1.772
42.077
1.6566
39.479
1.5543
40.129
1.5799
1.890
44.752
1.7619
41.866
1.6483
42.857
1.6873
2.047
48.752
1.9194
45.866
1.8057
46.587
1.8341
2.205
52.428
2.0641
49.252
1.9391
50.046
1.9703
2.362
56.428
2.2216
53.252
2.0965
54.046
2.1278
2.520
60.103
2.3663
56.639
2.2299
57.505
2.2640
2.677
64.103
2.5237
60.639
2.3874
61.505
2.4215
Drill
mm
0.75
0.85
0.95
1.1
1.25
1.45
1.6
1.75
2.05
2.5
2.9
3.3
3.8
4.2
5
6
6.8
7.8
8.5
9.5
10.2
12
14
15.5
17.5
19.5
21
24
26.5
29.5
32
35
37.5
40.5
43
47
50.5
54.5
58
62
Drill
Inch
0.030
0.033
0.037
0.043
0.049
0.057
0.063
0.069
0.081
0.098
0.114
0.130
0.150
0.165
0.197
0.236
0.268
0.307
0.335
0.374
0.402
0.472
0.551
0.610
0.689
0.768
0.827
0.945
1.043
1.161
1.260
1.378
1.476
1.594
1.693
1.850
1.988
2.146
2.283
2.441
Print Date: May 31, 2013
Pitch
Pitch
Automotive Service Solutions Confidential
QMS electronic document is the controlled copy
Page 13 of 21
Document No. PD0192 REV 4
Automotive Service Solutions QMS
METRIC THREAD -- FINE PITCH (1 mm - 18 mm)
Nominal
Size
mm
1.0 x 0.2
1.1 x 0.2
1.2 x 0.2
1.4 x 0.2
1.6 x 0.2
1.8 x 0.2
2 x 0.25
2.2 x 0.25
2.5 x 0.35
3 x 0.35
3.5 x 0.35
4 x 0.50
4.5 x 0.5
5 x 0.50
5.5 x 0.50
6 x 0.75
7 x 0.75
8 x 0.75
8 x 1.00
9 x 0.75
9 x 1.00
10 x 0.75
10 x 1.0
10 x 1.25
11 x 0.75
11 x 1.0
12 x 1.0
12 x 1.25
12 x 1.5
14 x 1.0
14 x 1.25
14 x 1.5
15 x 1.0
15 x 1.5
16 x 1.0
16 x 1.5
17 x 1.0
17 x 1.5
18 x 1.0
18 x 1.5
Major
Minor Dia Minor Dia Minor Dia Minor Dia
Tap
Tap
Diameter Diameter Diameter Male Thd Male Thd Fem Thd Fem Thd
Inch
mm
Inch
mm
Inch
mm
Inch
Drill
MM
Drill
Inch
0.8
0.9
1
1.2
1.4
1.6
1.75
1.95
2.1
2.6
3.1
3.5
4
4.5
5
5.2
6.2
7.2
7
8.2
8
9.2
9
8.8
10.2
10
11
10.8
10.5
13
12.8
12.5
14
13.5
15
14.5
16
15.5
17
16.5
0.031
0.035
0.039
0.047
0.055
0.063
0.069
0.077
0.083
0.102
0.122
0.138
0.157
0.177
0.197
0.205
0.244
0.283
0.276
0.323
0.315
0.362
0.354
0.346
0.402
0.394
0.433
0.425
0.413
0.512
0.504
0.492
0.551
0.531
0.591
0.571
0.630
0.610
0.669
0.650
0.039
0.043
0.047
0.055
0.063
0.071
0.079
0.087
0.098
0.118
0.138
0.157
0.177
0.197
0.217
0.236
0.276
0.315
0.315
0.354
0.354
0.394
0.394
0.394
0.433
0.433
0.472
0.472
0.472
0.551
0.551
0.551
0.591
0.591
0.630
0.630
0.669
0.669
0.709
0.709
Print Date: May 31, 2013
Pitch
0.87
0.97
1.07
1.27
1.47
1.67
1.838
2.038
2.273
2.773
3.273
3.675
4.175
4.675
5.175
5.513
6.513
7.513
7.35
8.513
8.35
9.513
9.35
9.188
10.513
10.35
11.35
11.188
11.026
13.35
13.188
13.026
14.35
14.026
15.35
15.026
16.35
16.026
17.35
17.026
Pitch
0.0343
0.0382
0.0421
0.0500
0.0579
0.0657
0.0724
0.0802
0.0895
0.1092
0.1289
0.1447
0.1644
0.1841
0.2037
0.2170
0.2564
0.2958
0.2894
0.3352
0.3287
0.3745
0.3681
0.3617
0.4139
0.4075
0.4469
0.4405
0.4341
0.5256
0.5192
0.5128
0.5650
0.5522
0.6043
0.5916
0.6437
0.6309
0.6831
0.6703
0.755
0.855
0.955
1.155
1.355
1.555
1.693
1.893
2.071
2.571
3.071
3.387
3.887
4.387
4.887
5.08
6.08
7.08
6.773
8.08
7.773
9.08
8.773
8.466
10.08
9.773
10.773
10.466
10.16
12.773
12.466
12.16
13.773
13.16
14.773
14.16
15.773
15.16
16.773
16.16
0.0297
0.0337
0.0376
0.0455
0.0533
0.0612
0.0667
0.0745
0.0815
0.1012
0.1209
0.1333
0.1530
0.1727
0.1924
0.2000
0.2394
0.2787
0.2667
0.3181
0.3060
0.3575
0.3454
0.3333
0.3969
0.3848
0.4241
0.4120
0.4000
0.5029
0.4908
0.4787
0.5422
0.5181
0.5816
0.5575
0.6210
0.5969
0.6604
0.6362
0.783
0.883
0.983
1.183
1.383
1.583
1.729
1.929
2.121
2.621
3.121
3.459
3.959
4.459
4.959
5.188
6.188
7.188
6.917
8.188
7.917
9.188
8.917
8.647
10.188
9.917
10.917
10.647
10.376
12.917
12.647
12.376
13.917
13.376
14.917
14.376
15.917
15.376
16.917
16.376
Automotive Service Solutions Confidential
QMS electronic document is the controlled copy
0.0308
0.0348
0.0387
0.0466
0.0544
0.0623
0.0681
0.0759
0.0835
0.1032
0.1229
0.1362
0.1559
0.1756
0.1952
0.2043
0.2436
0.2830
0.2723
0.3224
0.3117
0.3617
0.3511
0.3404
0.4011
0.3904
0.4298
0.4192
0.4085
0.5085
0.4979
0.4872
0.5479
0.5266
0.5873
0.5660
0.6267
0.6054
0.6660
0.6447
Page 14 of 21
Document No. PD0192 REV 4
Automotive Service Solutions QMS
18 x 2.0
0.709
Print Date: May 31, 2013
16.701
0.6575
15.546
0.6120
15.835
Automotive Service Solutions Confidential
QMS electronic document is the controlled copy
0.6234
16
0.630
Page 15 of 21
Document No. PD0192 REV 4
Automotive Service Solutions QMS
METRIC THREAD -- FINE PITCH (20 mm – 40 mm)
Nominal
Size
mm
20 x 1.0
20 x 1.5
20 x 2.0
22 x 1.0
22 x 1.5
22 x 2.0
24 x 1.0
24 x 1.5
24 x 2.0
25 x 1.0
25 x 1.5
25 x 2.0
27 x 1.0
27 x 1.5
27 x 2.0
28 x 1.0
28 x 1.5
28 x 2.0
30 x 1.0
30 x 1.5
30 x 2.0
30 x 3.0
32 x 1.5
32 x 2.0
33 x 1.5
33 x 2.0
33 x 3.0
35 x 1.5
35 x 2.0
36 x 1.5
36 x 2.0
36 x 3.0
39 x 1.5
39 x 2.0
39 x 3.0
40 x 1.5
40 x 2.0
40 x 3.0
Major
Pitch
Pitch
Minor Dia Minor Dia Minor Dia Minor Dia
Diameter Diameter Diameter Male Thd Male Thd Fem Thd Fem Thd
Inch
mm
Inch
mm
Inch
mm
Inch
0.787
19.35
0.7618
18.773
0.7391
18.917
0.7448
0.787
19.026
0.7491
18.16
0.7150
18.376
0.7235
0.787
18.701
0.7363
17.546
0.6908
17.835
0.7022
0.866
21.35
0.8406
20.773
0.8178
20.917
0.8235
0.866
21.026
0.8278
20.16
0.7937
20.376
0.8022
0.866
20.701
0.8150
19.546
0.7695
19.835
0.7809
0.945
23.35
0.9193
22.773
0.8966
22.917
0.9022
0.945
23.026
0.9065
22.16
0.8724
22.376
0.8809
0.945
22.701
0.8937
21.546
0.8483
21.835
0.8596
0.984
24.35
0.9587
23.773
0.9359
23.917
0.9416
0.984
24.026
0.9459
23.16
0.9118
23.376
0.9203
0.984
23.701
0.9331
22.546
0.8876
22.835
0.8990
1.063
26.35
1.0374
25.773
1.0147
25.917
1.0204
1.063
26.026
1.0246
25.16
0.9906
25.376
0.9991
1.063
25.701
1.0119
24.546
0.9664
24.835
0.9778
1.102
27.35
1.0768
26.773
1.0541
26.917
1.0597
1.102
27.026
1.0640
26.16
1.0299
26.376
1.0384
1.102
26.701
1.0512
25.546
1.0057
25.835
1.0171
1.181
29.35
1.1555
28.773
1.1328
28.917
1.1385
1.181
29.026
1.1428
28.16
1.1087
28.376
1.1172
1.181
28.701
1.1300
27.546
1.0845
27.835
1.0959
1.181
28.051
1.1044
26.319
1.0362
26.752
1.0532
1.260
31.026
1.2215
30.16
1.1874
30.376
1.1959
1.260
30.701
1.2087
29.546
1.1632
29.835
1.1746
1.299
32.026
1.2609
31.16
1.2268
31.376
1.2353
1.299
31.701
1.2481
30.546
1.2026
30.835
1.2140
1.299
31.051
1.2225
29.319
1.1543
29.752
1.1713
1.378
34.026
1.3396
33.16
1.3055
33.376
1.3140
1.378
33.701
1.3268
32.546
1.2813
32.835
1.2927
1.417
35.026
1.3790
34.16
1.3449
34.376
1.3534
1.417
34.701
1.3662
33.546
1.3207
33.835
1.3321
1.417
34.051
1.3406
32.319
1.2724
32.752
1.2894
1.535
38.026
1.4971
37.16
1.4630
37.376
1.4715
1.535
37.701
1.4843
36.546
1.4388
36.835
1.4502
1.535
37.051
1.4587
35.319
1.3905
35.752
1.4076
1.575
39.026
1.5365
38.16
1.5024
38.376
1.5109
1.575
38.701
1.5237
37.546
1.4782
37.835
1.4896
1.575
38.051
1.4981
36.619
1.4417
36.752
1.4469
Print Date: May 31, 2013
Automotive Service Solutions Confidential
QMS electronic document is the controlled copy
Tap
Drill
MM
19
18.5
18
21
20.5
20
23
22.5
22
24
23.5
23
26
25.5
25
27
26.5
26
29
28.5
28
27
30.5
30
31.5
31
30
33.5
33
34.5
34
33
37.5
37
36
38.5
38
37
Tap
Drill
Inch
0.748
0.728
0.709
0.83
0.81
0.79
0.91
0.89
0.87
0.94
0.93
0.91
1.02
1.00
0.98
1.06
1.04
1.02
1.14
1.12
1.10
1.06
1.20
1.18
1.24
1.22
1.18
1.32
1.30
1.36
1.34
1.30
1.48
1.46
1.42
1.52
1.50
1.46
Page 16 of 21
Document No. PD0192 REV 4
Automotive Service Solutions QMS
Formula for cutting Tap/Drill Sizes (Metric)
Drilled Hole Size (mm) = Basic Major Dia. of Thread (mm) - (% of Thread X mm Pitch) divided by 76.98.
Example: M10 x 1.5 tap and you want 75% threads.
Tap drill size would be 10mm minus, (75 x 1.5) divided by 76.98.
75 x 1.5 = 112.5. Divide that by 76.98 to = 1.461. Subtract that from 10mm = 8.53mm.
8.5 diameter drill will give you 75% threads.
NOTE: 60 – 80% of full thread is recommended.
Metric Form Tap - Drill Selector Chart
Metric
Size and
Pitch
M3 X 0.5
M3.5 X 0.6
M4 X 0.7
M4.5 X 0.75
M5 X 0.8
M6 X 1.0
M7 X 1.0
M8 X 1.25
M8 X 1.00
M10 x 1.5
M10 X 1.25
M12 X 1.75
M12 X 1.25
M14 X 2
M14 X 1.5
M16 X 2
M16 X 1.5
M18 X 2.5
M18 x 1.5
M20 X 2.5
M20 X 1.5
Drill
Size
7/64
3.2mm
27
4.10mm
4.60mm
5.50mm
6.50mm
L
7.50mm
9.20mm
U
7/16
.447
13mm
13.20mm
15.00mm
15.25mm
16.75mm
17.25mm
47/64
.757
Decimal
Equivalent
.1094
.1260
.140
.1614
.1811
.2165
.2559
.2900
.2953
.3622
.3680
.4375
.447
.5118
.5197
.5906
.6004
.6594
.6791
.7344
.757
Percentage
of Threads
65
73
72
78
73
74
73
74
73
78
77
74
76
73
78
73
73
74
74
78
76
ANSI B1 Report specifies a maximum and minimum internal minor diameter for class 6H threads.
In normal applications the above recommended drilled hole sizes will produce internal threads
which will meet these minor diameter gauging specifications.
Print Date: May 31, 2013
Automotive Service Solutions Confidential
QMS electronic document is the controlled copy
Page 17 of 21
Document No. PD0192 REV 4
Automotive Service Solutions QMS
Blank Diameters For Straight Rolled Threads
UNC & UNF ---- Class: 2 Steel
SIZE
10-15C SOFT
30 - 50C SOFT
30-50C OR
30-50C OR ALLOY
ALLOY 15-25RC
26-32RC
**STAINLESS
**STAINLESS
CHR. NICKEL CHR. NICKEL 400
300 SERIES
SERIES
MAX.
MIN.
MAX.
MIN.
Nom. Size.
T.P.I.
1/4 - 20
MAX.
MIN.
MAX.
MIN.
MAX.
MIN.
MAX.
MIN.
.2144
.2131
.2151
.2138
.2155
.2142
.2159
.2146
.2166
.2153
.2159
.2146
1/4 - 28
.2241
.2228
.2248
.2235
.2251
.2238
.2255
.2242
.2261
.2248
.2255
.2242
5/16 - 18
.2729
.2716
.2737
.2724
.2741
.2728
.2745
.2732
.2753
.2740
.2745
.2732
5/16 - 24
.2823
.2810
.2830
.2817
.2834
.2821
.2837
.2824
.2845
.2832
.2837
.2824
3/8 - 16
.3306
.3291
.3315
.3300
.3320
.3305
.3324
.3309
.3333
.3318
.3324
.3309
3/8 - 24
.3348
.3434
.3455
.3441
.3459
.3449
.3463
.3449
.3471
.3457
.3463
.3449
7/16 - 14
.3871
.3855
.3880
.3864
.3885
.3869
.3890
.3874
.3899
.3883
.3890
.3874
7/16 - 20
.4012
.3999
.4021
.4008
.4025
.4012
.4029
.4016
.4037
.4024
.4029
.4016
1/2 - 13
.4458
.4440
.4468
.4450
.4473
.4455
.4478
.4460
.4488
.4470
.4478
.4460
1/2 - 20
.4637
.4623
.4646
.4632
.4650
.4636
.4655
.4641
.4663
.4649
.4655
.4641
9/16 - 12
.5039
.5021
.5050
.5032
.5055
.5037
.5060
.5042
.5070
.5052
.5060
.5042
9/16 - 18
.5225
.5210
.5234
.5219
.5238
.5223
.5243
.5228
.5252
.5237
.5243
.5228
5/8 - 11
.5614
.5595
.5625
.5606
.5630
.5611
.5636
.5617
.5647
.5628
.5636
.5617
5/8 - 18
.5850
.5833
.5859
.5842
.5864
.5847
.5869
.5852
.5878
.5861
.5869
.5852
3/4 - 10
.6799
.6779
.6811
.6791
.6817
.6797
.6823
.6803
.6834
.6814
.6823
.6803
3/4 - 16
.7052
.7034
.7062
.7044
.7067
.7049
.7072
.7054
.7082
.7064
.7072
.7054
7/8 - 9
.7972
.7952
.7985
.7965
.7991
.7971
.7998
.7978
.8010
.7990
.7998
.7978
7/8 - 14
.8240
.8221
.8251
.8232
.8257
.8238
.8262
.8243
.8273
.8259
.8262
.8243
1-8
.9131
.9107
.9144
.9120
.9151
.9127
.9158
.9134
.9172
.9148
.9158
.9134
1 - 12
.9408
.9388
.9420
.9400
.9426
.9406
.9432
.9412
.9443
.9423
.9432
.9412
1-1/8 - 7
1.0262
1.0235
1.0276
1.0250
1.0283 1.0257
1.0290
1.0264
1.0304
1.0278
1.0290
1.0264
1-1/8 - 12
1.0657
1.0637
1.0669
1.0649
1.0675 1.0655
1.0681
1.0661
1.0693
1.0673
1.0681
1.0661
1-1/4 - 7
1.1510
1.1483
1.1525
1.1498
1.1533 1.1506
1.1540
1.1513
1.1555
1.1528
1.1540
1.1513
1-1/4 - 12
1.1906
1.1885
1.1919 1.1898
1.1925 1.1904
1.1931
1.1910 1.1943
1.1922
1.1931
1.1910
** Only certain grades can be rolled.
NOTE: These dimensions are for set-up reference only. Diameters must be finally established by actual
rolling and allowing for heat-treat and finish coatings as appropriate.
A rule of thumb process for figuring the turn diameter would be to use the lower limit of the pitch diameter + .002.
Print Date: May 31, 2013
Automotive Service Solutions Confidential
QMS electronic document is the controlled copy
Page 18 of 21
Document No. PD0192 REV 4
Automotive Service Solutions QMS
Bar or Turn Sizes for Rolled 6g Metric External Thread
Turn Dimension in Metric and Inches
Size
M5 X .8
M6 X 1
M8 X 1.25
M10 X 1.5
M10 X 1.25
M10 X .75
M12 X 1.75
M12 X 1.5
M12 X 1.25
M12 X 1
M14 X 2
M14 X 1.5
M15 X 1
M16 X 2
M16 X 1.5
M17 X 1
M18 X 1.5
M20 X 2.5
M20 X 1.5
M20 X 1
M22 X 2.5
M22 X 1.5
M24 X 3
M24 X 2
M25 X 1.5
Inch
.176 - .174
.210 - .208
.282 - .280
.354 - .352
.358 - .356
.372 - .370
.426 - .424
.430 - .428
.436 - .434
.443 - .441
.498 - .496
.508 - .506
.561 - .559
.577 - .575
.587 - .585
.640 - .638
.666 - .664
.721 - .719
.744 - .742
.758 - .756
.800 - .798
.823 - .821
.865 - .863
.887 - .885
.941 - .939
Metric
4.47 - 4.42
5.33 – 5.28
7.16 – 7.11
8.99 – 8.94
9.09 – 9.04
9.45 – 9.40
10.82 – 10.77
10.91 – 10.86
11.07 – 11.02
11.25 – 11.20
12.65 – 12.60
12.91 – 12.86
14.25 – 14.20
14.65 – 14.60
14.91 – 14.86
16.25 – 16.20
16.91 – 16.86
18.31 – 18.26
18.90 – 18.85
19.25 – 19.20
20.32 – 20.27
20.90 – 20.85
21.97 – 21.92
22.54 – 22.49
23.90 – 23.85
NOTE: These dimensions are for set-up reference only. Diameters must be finally established by actual
rolling and allowing for heat-treat and finish coatings as appropriate.
A rule of thumb process for figuring the turn diameter would be to use the lower limit of the pitch diameter +
.05mm (.002").
Print Date: May 31, 2013
Automotive Service Solutions Confidential
QMS electronic document is the controlled copy
Page 19 of 21
Document No. PD0192 REV 4
Automotive Service Solutions QMS
Threaded Rod
There are many types of threaded rod, but basically there are two materials that we normally use.
They are low carbon steel, and B7 alloy steel. The low carbon steel threaded rod is not manufactured
to the 2A thread classification and should be checked with 1A gauging. The B7 threaded rod,
manufactured to the ASTM193, Grade B7 standards, is per the 2A thread classification and should be
checked with 2A gauging.
Drawing call outs
There may be drawings with material (or an alternate material) of threaded rod, where as the part
calls for a –2A thread designation. If the material or alternate material used is threaded rod, it is to be
inspected to the mild steel threaded rod guidelines unless B7 is specifically called out.
Eng. ref: B7 is made from 4140 / 4142 high strength alloy with a tensile of 125,000 PSI. (Very similar
to grade 5 with approximate hardness of Rc 28-32.). Actual Specification is ASTM A 193, Grade B7.
Print Date: May 31, 2013
Automotive Service Solutions Confidential
QMS electronic document is the controlled copy
Page 20 of 21
Document No. PD0192 REV 4
Automotive Service Solutions QMS
General Purpose Acme Threads – single start
There are three classes of General-Purpose Acme threads, 2G, 3G, and 4G. It is suggested that
external and internal threads of the same class be used together for general-purpose assemblies,
Class 2G being the preferred choice. If less backlash or endplay is desired, Classes 3G and 4G
are available.
External General Purpose Acme Threads – 2G single start
Size
TPI
Type
Lead
Major Diameter
Pitch Diameter
Minor Diameter
Max.
Max.
Max.
Min.
Min.
Min.
3/16
20
std.acme
0.0500
0.1870
0.1820
0.1600
0.1500
0.1270
0.1120
1/4
16
std.acme
0.0620
0.2500
0.2450
0.2140
0.2040
0.1770
0.1610
1/4
20
std.acme
0.0500
0.2500
0.2450
0.2210
0.2110
0.1900
0.1750
3/8
8
stubacme
0.1250
0.3750
0.3680
0.3320
0.3180
0.2800
0.2650
3/8
10
std.acme
0.1000
0.3750
0.3700
0.3200
0.3060
0.2550
0.2350
3/8
12
std.acme
0.0830
0.3750
0.3700
0.3280
0.3160
0.2810
0.2630
3/8
16
std.acme
0.0630
0.3750
0.3700
0.3380
0.3270
0.3020
0.2850
3/8
20
std.acme
0.0500
0.3750
0.3700
0.3450
0.3340
0.3150
0.2990
1/2
10
std.acme
0.1000
0.5000
0.4950
0.4440
0.4300
0.3800
0.359
5/8
8
stubacme
0.1250
0.6250
0.6180
0.5810
0.5650
0.5300
0.5140
5/8
10
std.acme
0.1000
0.6250
0.6200
0.5680
0.5540
0.5050
0.4830
3/4
5
std.acme
0.2000
0.7500
0.7400
0.6430
0.6240
0.5300
0.5020
3/4
6
std.acme
0.1670
0.7500
0.7410
0.6590
0.6420
0.5630
0.5370
3/4
8
std.acme
0.1250
0.7500
0.7430
0.6800
0.6640
0.6050
0.5810
7/8
4
stubacme
0.2500
0.8750
0.8620
0.7920
0.7710
0.7050
0.6840
7/8
5
std.acme
0.2000
0.8750
0.8650
0.7670
0.7480
0.6550
0.6260
7/8
6
std.acme
0.1670
0.8750
0.8660
0.7840
0.7660
0.6880
0.6610
7/8
8
std.acme
0.1250
0.8750
0.8660
0.8050
0.7880
0.7300
0.7050
7/8
10
std.acme
0.1000
0.8750
0.8700
0.8170
0.8020
0.7550
0.7320
1
5
std.acme
0.2000
1.0000
0.9900
0.8920
0.8720
0.7800
0.7500
1
8
std.acme
0.1250
1.0000
0.9930
0.9290
0.9120
0.8550
0.8300
Formula to calculate tap drill size for acme taps based on a 100% of thread as per ANSI.
Step 1) Divide “1” by the pitch
Step 2) Subtract this amount from the OD. For pitches 10 and greater, add .005" to the drill size. For pitches less
than 10 TPI, take the amount from step 2 and multiply x .05 (5 %) and add this to the drill size. (This is for
95% to 100% threads.)
Example for 3/4-6 ACME-2G
1 divided by 6, or 1/6, = .167
.750 - .167 = .583" (100%)
.167 X .05 = .008" (to obtain 5%)
.583 + .008 = .591" (95%) Use the closest size drill bit available to obtain this tolerance.
Print Date: May 31, 2013
Automotive Service Solutions Confidential
QMS electronic document is the controlled copy
Page 21 of 21