ASSUMPTION UNIVERSITY
Faculty of Engineering
Physics Laboratory
Name:_________________________________________ Code:_________________ Sec:______
1. Experiment
: Screw gauge (micrometer screw gauge).
2. Objective
: To determine the dimension of the small objects by using micrometer screw
gauge.
3. Apparatus
: Screw gauge, ball bearing, metal wire and digital scale.
4. Theory
: The screw gauge (or) micro meter screw gauge is a simple instrument of much
importance. Screw gauge (or) micro meter screw gauge enables us to obtain accurately up to the
second decimal place in millimeter. (e.g. 0.01 mm) [(or) up to the third decimal place in
centimeter measurement.]
The sleeve scale is marked on the sleeve potion of the instrument and thimble scale
is marked on the circular potion (thimble part) of the instrument. The sum of sleeve scale
measurement, thimble scale measurements and zero error correction of the micro meter screw
gauge is the required dimension of the measurement of an object
To use the micro meter screw gauge Least count (LC) and Zero error reading (or)
zero error correction of micrometer screw gauge must be checked and recorded before
measuring the object
(a) Least Count of micrometer screw gauge
When thimble is rotated just one circular division, the distance between anvil and spindle
is the smallest measurement (or) least count (LC) that can measure by micrometer screw gauge.
The least count [LC] of micrometer screw gauge can be calculated as pitch of the thimble
divided by the number of circular thimble divisions.
When one complete rotation of the thimble (50 division of thimble scale) is rotated, the
movement of spindle to anvil is called pitch of the thimble. That distance can be measured by the
movement of edge of thimble on the sleeve as 0.5mm.
The pitch of the thimble = 0.5 mm
The number of circular divisions of thimble = 50
The distance movedby thimble when it rotates just one circular division 
least count ( LC ) of micrometer screw gauge 
pitch of the thimble
number of thimble divisions
pitch of the thimble
number of thimble divisions
0.5mm
 0.01 mm
50
The least count [LC] of micrometer screw gauge  0.01 mm
Least Count LC 
A measuring instrument cannot measure anything whose dimensions are less than the
magnitude of least count. The instrument will have more precise measurement if the magnitude of
least count is smaller value.
(b) Zero error reading of micrometer screw gauge (  zero error correction of measurement )
When the anvil and the spindle are just in contact by using ratchet, the number of
thimble scale divisions which are getting difference upward or down ward position with
respect to the datum line is called “zero error reading of micrometer screw gauge”.
1. When the anvil and the spindle are just in contact by using ratchet, if the zero mark on
the circular thimble scale coincides with the datum line on the sleeve, the value of zero
error reading is zero or no zero error correction.
2. When the anvil and the spindle are just in contact by using ratchet, if the zero mark on
circular thimble scale lies below the datum line on the sleeve, the number of circular
thimble scale divisions between datum line and thimble scale zero is counted. This
counted number of circular thimble scale divisions gives the negative value zero error
reading of micrometer screw gauge. [-1, -2, -3, -4 ...etc.]
3. When the anvil and the spindle are just in contact by using ratchet, if the zero mark on
circular thimble scale lies above the datum line on the sleeve, the number of circular
thimble scale divisions between datum line and thimble scale zero is counted. This
counted number of circular thimble scale divisions gives the positive value zero error
reading of micrometer screw gauge. [+1, +2, +3, +4 ...etc.]
To get zero error correction of the measurement, zero error reading of thimble
scale divisions must be multiply by least count (LC) of the micrometer screw gauge.
Examples of zero error readings for micrometer screw gauge
0
0
The zero mark on the circular scale coincides with the datum line on the
sleeve; the value of zero error reading is zero.
0
5
0
The required measurement is longer than the actual length. The longer length
is between zero mark of thimble scale and the datum line; because the
measurement must be started from zero mark of thimble scale and datum
line marks together. The longer length can be calculated by number of
thimble scale divisions below the datum line times of least count and that
longer length must be subtract from the total measurement.
Zero error negative value =  3 x LC mm.
0
0
45
The required measurement is shorter than the actual length. The shortening
length is between zero mark of thimble scale and the datum line; because
the measurement must be started from zero mark of thimble scale and
datum line marks together. The shortening length can be calculated by
number of thimble scale divisions above the datum line times of least count
and that shorter length must be added to the total measurement.
.
Zero error positive value = + 3 x LC mm.
Measurement of objects by using micrometer screw gauge
To measure the dimension of an object by using the micrometer screw gauge, the object
must be placed between anvil and spindle by using ratchet without over force until object is secured
and then need to take two measurements by using two scales, sleeve scale and thimble scale.
(1) Sleeve scale reading (sleeve scale measurement)
After placing the object between anvil and spindle by using ratchet sleeve scale reading is
taken full number of sleeve scale divisions on the sleeve at the edge of the thimble without estimation.
Check the complete number of sleeve scale divisions on the datum line both upper and lower position
up to 0.5 without estimation. This reading will give the sleeve scale reading. To get the sleeve scale
measurement sleeve scale reading must be multiplied by 1mm; because one division of length on
sleeve portion is 1mm for both upper scales and lower scale on the datum line.
Note that under the datum line, half scale division (0.5 mm) must be included in the
sleeve reading, if the whole line of 0.5 mm mark on the sleeve scale is visible under the edge of
the thimble by reading without parallax error.
(2) Thimble scale reading and thimble scale measurement
After placing the object between anvil and spindle by using ratchet the circular thimble scale
line that coincides with the datum line is the thimble scale reading. If datum line does not coincide
with thimble scale line, take the nearest value of thimble scale. Two significant figures (hundredths of
a millimeter) are taken from the thimble scale measurement or simply thimble scale reading.
The distance moved by the thimble when it is rotated just one circular division is the least
count (LC) of the micrometer screw gauge therefore to get the thimble scale measurement, thimble
scale reading must be multiplied by least count (LC).
(3) Measurement of objects by using micrometer screw gauge
The sum of the sleeve scale measurement, thimble scale measurement and zero error reading (or)
zero error correction of the screw gauge is the measurement of the required dimension of the object.
The required measurements for the dimension of the object are,
(1) Measurement by sleeve scale
[Sleeve scale reading (number of both sleeve scale divisions without estimation) x 1mm],
(2) Measurement by thimble scale
[Thimble scale reading (number of thimble scale divisions) x Least count (LC))]
(3) Zero error correction of the measurement
[  zero error reading (± number of thimble scale divisions) x Least count (LC)]
5. Instructions
1. Find the least count (LC) of the micrometer screw gauge and record at the proper place.
2. Find Zero error reading when the anvil and the spindle are just in contact by using ratchet
and record in the data table.
3. Measure two trials for diameter of metal ball. Metal ball is placed between anvil and spindle
by using ratchet without over force. When metal ball is secured by using ratchet then take
sleeve scale reading at the edge of thimble on the sleeve and take thimble scale reading at
datum line position on the thimble sale on the thimble. Record the all data in the table.
4. Measure two trials for diameter of metal wire. Straight part of metal wire is placed between
anvil and spindle by using ratchet without over force. When metal wire is secured by using
ratchet then take sleeve scale reading at the edge of thimble on the sleeve and take thimble
scale reading at datum line position on the thimble sale on the thimble. Record the all data
in the data table.
5. Find the sum of (a) sleeve scale measurement, (b) thimble scale measurement and (c) Zero
error correction of the measurement to get the measurement of the required dimension.
Record the all data in the data table
6. Measure the mass of metal ball and mass of the metal wire by using electronic digital scale.
Record the all data under the data table.
Assignment questions
1. Calculate the followings.
(a) Radius of the metal ball.
(b) Volume of the metal ball.
(c) Density of metal ball.
(d) Radius of the metal wire.
(e) Cross sectional area of the metal wire.
(f) If the length of wire is 5 cm, find the volume of the wire.
2. How can you take sleeve scale reading of an object by using a micro meter screw gauge?
3.
How can you take thimble scale reading of an object by using a micro meter screw gauge?
4. Explain least count of micro meter screw gauge
5. How can you calculate the least count of a micro meter screw gauge?
6. Explain zero error reading and types of zero error reading of micro meter screw gauge?
7. The result obtained when measuring a small object by using a micrometer screw gauge with
least count value of 0.01mm is 2.423 cm;
(a) Is it the reasonable measurement by using given micrometer screw gauge, yes or no?
Explain to support your answer.
(b) How many significant figures are there in this case?
(c) What is the doubtful (uncertain) figure?
(d) Give the result in scientific notation.
8. The following diagrams (a) is showing zero error reading of micrometer screw gauge, diagrams
(b) is showing sleeve and thimble positions when a small metal ball is between anvil and
spindle without over force. Find the measurement (diameter) readings for the following
diagrams. Answer should be included according to the following steps in scientific notation
and SI unit.
Least count (LC) of micrometer screw gauge =
Sleeve scale measurement =
Thimble scale measurement x LC =
Zero error correction of measurement x LC =
Measurement (diameter) of metal ball =
0
5
0
(a) Zero error reading
0
25
20
(b) Measurement reading for an object
9. You are given a sufficiently long piece of thread, a meter stick and a thin round shape iron rod.
Explain how would you measure the diameter of iron rod by using given thread and meter
stick.
(Hint: you can’t put the cotton wire to be correct position of diameter of the iron rod.
You should use another way to measure the diameter of iron rod)
Name:_________________________________________ Code:_________________ Sec:______
Data taking
Micrometer screw gauge
Object : :METAL BALL
Least Count (LC) = ____________________
Measurements
Diameter
Sleeve scale reading x 1 mm
(sleeve scale measurement)
Thimble scale reading x LC mm
(thimble scale measurement)
() Zero error reading x LC mm
(Zero error correction of measurement)
mm
..... x 0.01mm

x 0.01mm
Total measurement in mm
Average measurement in mm
Average measurement in m
Mass of the metal ball
=
g =
kg
Object : :METAL WIRE
Measurements
Sleeve scale reading x 1 mm
(sleeve scale measurement)
Thimble scale reading x LC mm
(thimble scale measurement)
() Zero error reading x LC mm
(Zero error correction of measurement)
Total measurement in mm
Average measurement in mm
Average measurement in m
Mass of the metal wire
=
Diameter
Some concepts, important points and examples for micro meter screw gauge
(Don’t use for your report.)
Micrometer screw gauge
The Micrometer screw gauge is a simple instrument of much importance. It enables us to
obtain accurately up to the third decimal place in centimeter measurement. [See figure.]
Datum line
On the sleeve portion, it consists a linear scale division of 1mm (0.5 mm position
starts under the datum line.) and maximum 25mm length is calibrated. A screwed spindle,
which is fitted with a graduated circular scale with 50 divisions, is called thimble. The
distance moved by the thimble for one complete rotation (50 divisions) of it is called the pitch
of the thimble and it is found to be 0.5 mm.
Important points to take sleeve reading and thimble reading
a.
Sleeve scale reading - the first significant figure is taken from the last graduation showing on
the sleeve directly to the left of the revolving edge of the thimble is the sleeve reading. If 0.5
sale line of the mark on the sleeve scale is visible at the edge of the thimble an additional half
scale division (0.5 mm) must be included in the sleeve reading. To get the correct reading
observe the edge of thimble position directly above the thimble and check can see the complete
sleeve scale line without parallax error .
Sleeve scale reading multiplied by 1mm will give the sleeve scale measurement.
b. Thimble reading - The (thimble scale) circular division that coincides with the datum line is
noted and the reading is taken is the thimble scale reading. Take the nearest value of thimble
scale if datum line is not exactly the same position with the thimble division.
Thimble scale reading multiplied by the least count will give the thimble measurement.
Important points for handling the micrometer screw gauge
In order to measure an object, the object is placed between anvil and spindle and
thimble is rotated using the ratchet until the object is secured. Do not handle and rotate
thimble. Hold the ratchet and turn until the object is lightly gripped.
1. DO NOT OVERTIGHTEN BY THE THIMBLE. Do not handle and rotate thimble.
2. Note that the ratchet knob must be used to secure the object firmly between anvil and
spindle, otherwise the instrument could be damaged or give an inconsistent reading. The
manufacturer recommends maximum 3 clicks of the ratchet before taking the reading.
3. The lock may be used to ensure that the thimble. Do not rotate thimble while the lock screw is
used and while you take the reading.
Example of measurement taken by micrometer screw gauge:
Find the measurement for the following positions of micrometer screw gauge.
0
5
0
45
0
Zero error reading
0
measurement reading for an object
The following readings can be seen on the above diagram.
(1). Sleeve scale measurement
= 2 .5 sleeve scale reading x 1mm = 2.5 mm
[ Note:- Be included 0.5 value of sleeve scale if the whole scale division line can be seen.]
(2). Thimble scale measurement
= 48 thimble scale reading x LC
= 0.48 mm
[Thimble scale reading x LC = 48 x 0.01 mm]
(3). Zero error correction of measurement = () zero error reading x LC
=  0.03 mm
[Zero error reading x LC = 3 x 0.01 mm]
The sum of (1) sleeve scale measurement (2) thimble scale measurement and (3) zero error
correction of measurement (positive or negative value) will give the required measurement of the
length by using micrometer screw gauge.
Measurement of objects by using micrometer screw gauge
(1) Sleeve scale measurement
2 .5 x 1 mm
= 2.50 mm
(2) Thimble scale measurement
48 x 0.01 mm = 0.48 mm
(3) Zero error correction of measurement 3 x 0.01 mm = 0.03 mm
-----------------------------------------Measurement of an object
= 2.95 mm (or) 2.95 x 10-3m