This stainless streel precision machinist square is perfect for the professional machinist, meticulous wood worker, or the DIY perfectionist. It is cut and ground from a solid blank of 6 mm (.220 inch) thick stainless steel. All faces and edges are ground and lapped for straightness and parallelism. There is a groove milled in the inner corner to provide clearance for burrs and debris. Manufactured to strict DIN 875/0 standards and guaranteed square to within 8 microns or 0.0005 inches (that’s 5 ten-thousandths of an inch).