Depth micrometerAs the name implies, it was designed to measure the depth of holes, grooves, gaps, keyways, etc. There are versions with analog reading and also, some more modern, with digital reading.
This measuring instrument consists of a hardened, ground and polished base, combined with a micrometer head. The rods are inserted through an existing hole in the micrometer spindle, and are placed in the correct position by means of a knurled nut.
The micrometric spindle is ground, with high precision, and has a course that is usually 25mm or 1 “. The rods are provided with differences of 25mm (or 1”) each. Each rod emerges from the base and advances according to the rotation of the drum.
The reading is obtained in exactly the same way as an outside micrometer, except that in this case, the cylinder has the graduation in the opposite direction.
Before using a depth micrometer, make sure the base, rod tip, and workpiece are clean, and that the rod is properly seated in the micrometer head.
When measuring, firmly hold the base of the micrometer against the base of the object to be measured, as shown in the video below. Rotate the drum until the rod bottoms out, engage the lock and remove the micrometer to take a reading.
Video: How to use a depth micrometer?
With frequent use, wear may arise, to compensate for them, certain models have the option of making adjustments from a nut located at the top of the rod. Whenever you make any changes, then verify the calibration using a gauge block.