Made in McKees Rocks, PA. Great for structural steel, pipe fitting, sheet metal work and carpentry. Designed with 4 - 90 degree angles for squaring and marking work points around an edge or insert. 1 9/16" opening by 3 1/2" deep. Used for stair stringers and stair spindle layouts plus 2x4's notch outs. Zero/zero center finding ruler for your work materials. T-square effect design. 3 points of centering. Regular squaring. Finds the depth for striking nails on an overhanging edge or insert. You can also transfer work points from far side to near side for layout purposes. Measures height and depth simultaneously.