A T-square attachment for standard 12mm steel rulers allowing for accurate sketches on the go. Pairs well with triangles and a french curve scaled to an appropriate size. One STL is a proper T-square and one is a combo square with a 45 degree angle. Both print as a top and bottom with holes for screwing together and a hole for a set screw to tension the ruler in place. If the fit is loose a small piece of electrical tape in the ruler groove will help keep in place. All holes will likely need post processing.