Depth gauge
a gauge for measuring the depth of holes, grooves, or concavities.
Another type of micrometer is a depth micrometer. It is an accurate and reliable tool for depth measurement. This micrometer is used to find the distance between two parallel surfaces i.e. depth of holes, slots, shoulders and projections. This micrometer has the same thimble and sleeve as outside micrometer.
an instrument to measure or find the depth or quantity of water or to indicate the height of its surface especially in a steam boiler.