Ever wonder why every contractor you see has a triangular square stuck in his tool belt? This dandy little tool is often called a speed square, and it can offer you the biggest bang for the buck in your toolbox. I picked up the one shown in the photos for $3 at a home center in 1999. This tool has dozens of uses; here are three of our favorites.
Place the pivot point against the shingles. Then place a torpedo level on the fat base of the square and adjust the square until the level is level. Read the pitch on the side of the square.
With a torpedo level and a speed square, you can pretty accurately gauge the pitch of any roof with a gable end (Photo 1). The pitch tells you the amount of vertical rise (in inches) for every 12 in. of run. To find the pitch, just place the pivot point against the shingles. Then place a torpedo level on the fat base of the square and adjust the square until the level is level, and read the pitch on the side of the square.
You can use the speed square to mark an angle, such as when cutting a rafter tail, by holding the pivot point against the board. Swing the square until you read the desired angle on the board’s edge, and make your mark. Photo 2 shows how to use the speed square to mark a 33-1/2 degree angle—the same, as you would need on a rafter tail for a roof with an 8/12 pitch.
Before miter saws, and even since, professional carpenters used speed squares as a quick saw guide for cutting 45- and 90-degree angles. The plastic squares are thicker than most metal ones, making them a good fence for the shoe of a circular saw to ride along. This method works better (and safer) when right-handed users have a circular saw with the motor to the right of the blade (like the one in Photo 3).
Here are some other quirky uses we’ve heard speed squares put to: nail set, boot scraper, shim, butter knife and digging tool. It’s a good thing they don’t cost much.
Original article and pictures take http://www.familyhandyman.com/tools/how-to-use-a-speed-square/view-all site