The Precision Square is ideal for any application where accurate right angles are essential. The ground and polished carbon steel blade is securely riveted to the beam, and can be used for marking and checking both internal and external 90 degree angles. In addition, a groove on the inside corner of the beam provides clearance of any dirt or burrs on an imperfect work piece. For checking internal and external 90 degree angles. Fully ground and polished carbon steel blade. Beam is riveted securely to blade. Blade length is 6-1/4 in. Beam length is 3-1/4 in. Groove on inside corner of blade provides clearance of dirt and burrs.