Swanson S0101 7 in Speed Square with Blue Book

A speed square looks like a simple triangle, but it replaces several tools on a DIY project. Hold it against the edge of a board and you can mark a square line, a 45° line, or any angle on the protractor scale. Press it against the board and run a circular saw along it, and it’s a saw guide for clean, square cuts.

The row of notches is the hidden trick: put a pencil in a notch and slide the square along the edge to draw a line parallel to it, which is handy for ripping a board or marking a reveal.

Pro tip To make a square cut with a circular saw, hold the square’s lip firmly against the far side of the board and keep the saw’s base plate pressed against the square’s edge for the whole cut.