Want to make your own?
Buy the FILES we used to cut out our squares and bring them to your local laser or plasma cutter - https://www.etsy.com/listing/1182088004/diy-welding-square-files-for-laser-or?ref=listings_manager_grid
You will need: the file, a plasma or laser cutter, and flat plat - 1/8 to 1/4" thick. I used 2" by 1/4" bar stock for the outside perimeter.
Let's make welding squares! We cut these plates out of steel on the plasma table and are welding them up into squares. Use these to make things perpendicular easily with no hassle!