Is Your Square Square?
Framing squares—even brand-new ones—aren’t reliably square.
1 To test your square, place the tongue (the short part) against the factory edge of a sheet of plywood and make a line along the body (the long part) using a sharp pencil.
2 Flip the square and line up the body with the line you just made. If it lines up perfectly, you have a square square.
3 If it doesn’t line up perfectly, you can try to fix it (next step). You’ll need a center punch, a hammer and something to use as an anvil, such as your vise (a wood surface doesn’t work).
4 If your square is less than 90 degrees, set it on your “anvil” and punch the inside corner hard enough to make a dimple. Squeezed between the punch and the anvil, the metal moves outward. Recheck the square, starting with a new line. Increase the dimple as needed, rechecking each time you strike the square.
5 If your square is more than 90 degrees, dimple the outside corner.
If you’re shopping for a new square, grab a handful of them, take them to the plywood aisle, sharp pencil in hand, and test them first.