Constructed from hardened carbon steel, with high tolerance and ground surface and edges, this 90 engineer/machinist square is ideal for design work. This tool helps with making perfect 90 right angles. German DIN Standard 875 Grade 1. Square Dimensions: 4″ (100 mm). Base Thickness: 15/32″ (11.86 mm). Square Tolerance: 0.0002″. Straightness Tolerance: 0.0005″.