Mitre box

A mitre box (US spelling, "miter box") is a wood working tool used to guide a hand saw to make precise mitre cuts in a board.

The most common form of a mitre box is a 3-sided box which is open at the top and the ends. The box is made wide enough to accommodate the width of the boards to be cut. Slots are cut in the walls of the box at the precise angle at which the cut is to be made. These slots provide the guide for the saw to follow. Most commonly, the slots in the mitre box are cut at 45 degrees and 90 degrees.