A sliding T bevel, also known as a bevel gauge or false square is an adjustable gauge for setting and transferring angles. The handle is usually made of wood or plastic and is connected to a metal blade with a thumbscrew or wing nut. The blade pivots and can be locked at any angle by loosening or tightening the thumbscrew.
The bevel can be used to duplicate an existing angle, or set to a desired angle by using it with any number of other measuring tools (such as a protractor, or framing square).