A flush pin gauge is used for checking ______ of hole. 

Explanation:

Flush Pin Gauges

• These types of gauges are mainly used to check the depths of slots, but can also be used for gauging lengths and tapers.
• A flush pin is defined as a gauge for checking the distance between two surfaces, comprising a body having a through-the-hole, and a pin in the hole which projects from the face of the body, a distance equal to the dimension to be gauged when the opposite or indicating end of the pin is flush with the opposite face of the body.
• The indicating end of the pin, or the adjacent face of the body. has a step of a depth equal to the tolerance on the dimension gauged.