The depth micrometer is a tool used to measure the distance between two parallel surfaces. Depth micrometers have the same thimble and sleeve as other micrometers and are made to take readings in either inch or metric units. They come in sets with different length depth rods for different ranges of measurement.
To measure with a depth micrometer , place the base on one surface to be measured . Then rotate the thimble to move a depth rod down to the lower surface. The distance the rod moves down is the depth. The depth is read just like any micrometer measurement on the thimble and sleeve.