Action gauge

A flat graduated rule, marked in millimetres and usually in 64ths of an inch, used to read string height, relief and fret height accurately.

It is the cheap tool that turns setup from guesswork into measurement. The rule rests across two frets or on the frets either side of the fret being checked, and the graduations are fine enough to read a few thousandths of an inch. Because the numbers are the same everywhere, a setting you measure can be repeated later, or passed to a tech, which is impossible with a description like "about right".

Example: an action gauge dropped on the frets at the twelfth fret reads string height directly, which is how a player confirms a factory setup before deciding whether to shim the neck.

Action gauge

See also