Squares have accurate right angles both inside and outside. Made from a single piece of fully tool steel. Beams and blades are ground and accurately lapped for straightness and parallelism. Accuracy Class H Blades are beveled on both edges of each side. Beam is grooved at inner comer for clearance of burr and dirt. All squares are fully hardened (Rockwell 55). Packed in indiviual cartons. Accuracy 0.02MM