Mitre square

Also called: miter square

A mitre square is a hand tool for marking and checking the diagonal cut across the end of a board.

The fixed angle

Its blade is fixed at 45 degrees to the stock, the handle that you hold against the board. A try square, a tool for marking a right angle, has a different setting, so do not use one as though it were a mitre square.

Mark a mitre

Set the handle against the arris, the sharp corner where two faces meet, and slide the square until the sloping blade reaches the required position. Draw along the blade to mark the cut. Turn the square when the diagonal needs to run in the opposite direction.

Check the tool

Before relying on the square, compare its blade with an accurate 45-degree reference. A combination square, a square with a separate adjustable head, can provide that check. A small error at the tool becomes an error in every mitre it marks.