Micrometer Depth Gauge (Fig. 2.128) (Metrology)

2.42.
It is used for measuring the depths of holes, slots and
recessed areas. It has got one shoulder which acts as refer-
ence surface and is held firmly and perpendicular to the
centre line of the hole. Here also for larger ranges of meas-
urements, extension rods are used. The screw of micrometer
depth gauge has range of 20 mm or 25 mm. The length of
the micrometer depth gauge varies from 0 to 225 mm. The
rod is inserted through the top of the micrometer. The rod is
marked after every 10 mm so that it could be clamped at any

Fig. 2.128. Micrometer depth gauge.
position. In using this instrument, first it must be ensured that the edge of the hole is free from
burrs.
The scale here is calibrated in the reverse direction. The accuracy again depends upon the
sense of touch.