The presentation is meant for grade 10 or O Level physics students

1. TOPIC FOR CLASS IX -X
OR
CAMBRIDGE IGCSE
O-LEVEL
Micrometer Screw Gauge
~Dr Lalit Kishore, Plenum School, HP

2. Screw gauge
 A distance/length measuring instrument that
measures with least count (LC) of micrometer (one
millionth of a metre)
 Least Count
 One hundredth of mm
 One thousandth of cm
 One ten-thousandth of decimetre
 One hundred-thousandth of meter or 10 raised power minus 5
metre or micrometer

3. Two scales of a screw gauge
 Main scale in mm
 Fractional or circular scale 50 or 100 divisions (In
schools labs 100 divs on circular scale are common)
 Screw principle: On complete turn of circular scale or
100 divs is equal to 1 mm
 One div. turn of circular scale is 1 mm / 100
 LC of screw gauge: 1/100 mm or .01 mm
 For example 23 div. turn of circular scale equals .25 mm

4. Diagram of screw gauge
 1. Rod for measuring
diameter
 2’ & 2 Jaws
 3. Screw
 4. Main scale
 5. Fractional / circular
scale
 6. Rotating barrel
 7. Friction clutch

5. Learning to draw diagram of screw gauge: Six-
step successive drawing

6. A typical reading

7. Lab procedure for measuring diameter of a wire
or thin rod
 Put the rod between the
two jaws of the screw
gauge
 Turn the circular scale
barrel till the jaws just
grip the rod
 Read the main scale to
the nearest mm count
 Read the additional
fraction of an mm from
fractional scale