The Outside Micrometer
Everything you need to know
about the Imperial micrometer
1
2
2”-3”
1”-2”
0-1”
Calibration
standards
Spanner
wrenches
3
The Fundamentals
Parts of a micrometer
How to hold a micrometer
How to position the measuring faces
How tight when measuring
How to read an imperial micrometer
Accuracy to 0.001 of an inch
Imperial micrometer
Sleeve
Has 40 graduations along its length of 1
inch
Each graduation is 1/40 of an inch
=0.025inches
Every 4th graduation is larger =1/10 of
an inch or =0.1 inch
The Thimble
This is the part that is turned
The thimble scale has 25 graduations
around the thimble that is numbered 025
Each graduation =0.001 inch
This gives accuracy to 0.001 inch
The Ratchet
Located at the end of the thimble
Used to control the force or load applied to
the micrometer while measuring
Prevents the micrometer from being over
tightened
When max load is reached it will make a
clicking sound. Some types use a sliding
clutch
The spindle
The spindle is a plunger that moves in a
linear direction
One revolution of the thimble moves
the spindle 0.025” or 1 graduation on
the sleeve
The spindle carries one of the
measuring surfaces that contacts the
object being measured
The Frame and Anvil
The frame is the main support member
for all other parts of the micrometer
The anvil is located in the far end of the
frame and provides the fixed measuring
surface
The frame will have the size and type of
micrometer marked on it
They are usually made from cast iron
The lock
May be of a lever or a roll type
Locks the spindle to the sleeve so that
readings can be taken easily
Allows you to capture the reading of the
scales
How to hold a micrometer
Positioning
How to Read a micrometer to .001”
Sleeve: The micrometer sleeve is divided into forty equal
parts. Each part or division is indicated by a vertical line.
Each line represents one-fortieth of an inch or .025” and each
fourth line is marked with a longer line which designates one
hundred-thousandths.
Simplified, the line marked “1” represents .100”, the line
marked “2” represents .200” and so forth.
Thimble: The thimble is divided into twenty-five equal parts
and one complete rotation of the thimble coincides with the
smallest division on the sleeve. Thus the division on the
thimble is one-twenty-fifth of .025” or .001”.
Reading Example: (see illustration to right)
1. Note that the thimble has stopped at a point beyond “2”
on the sleeve indicating .200”.
2. Note that one additional line is visible between the
graduation numbered “2” and the edge of the thimble ,
indicating .025”.
3. The line numbered “1” on the thimble coincides with the
line on the sleeve. It means an additional one-thousandth
of an inch.
_________________________________________________
1) Reading on the sleeve…………………….. .200”
2) No. lines between “2” and
the edge of thimble……………………….. .025”
3) Thimble line corresponding
to center line of sleeve…………………… .001”
TOTAL READING…………………….. .226”
How to Read a micrometer to .0001”
To read to one ten-thousandth of an inch requires an additional
scale called the “Vernier” scale, named after the inventor, Pierre
Vernier.
In the case of a regular micrometer, the Vernier consists of ten
divisions, marked on the sleeve. Which are spaced within nine
divisions of the thimble scale.
Therefore each division on the Vernier is one-tenth shorter than
that of the thimble’s, thus representing .0001”.
Reading Example: (see illustration to right)
1. Note that the thimble has stopped at a point beyond “2” on
the sleeve indicating .200”.
2. Note that one additional line is visible between the
graduation numbered “2” and the edge of the thimble ,
indicating .025”.
3. The line numbered “1” on the thimble coincides with the
line on the sleeve. It means an additional one-thousandth of
an inch.
4. Note that the Vernier line numbered “2” coincides exactly
with the thimble line indicating .0002”.
_________________________________________________
1) Reading on the sleeve…………………….. .200”
2) No. lines between “2” and
the edge of thimble……………………….. .025”
3) Thimble line corresponding
to center line of sleeve…………………… .001”
4) Vernier line coincides exactly
with thimble line………………………… .0002”
TOTAL READING…………………….. .2262”
Let’s practice what we have learned
Let’s practice what we have learned
.225
.200
.487
.250
.304