2 3/8" wide hardened steel base Spring tension nut 6" Etched stainless steel rule Graduated in 64ths and mm on other side Has 2 3/8" wide hardened steel base. Spring tension nut eases depth and angle measuring by securing rule in milled slot at 90 degree to base. Permits easy setting of protractor angle to 30 degree, 45 degree and 60 degree settings on one side. 6" etched stainless steel rule graduated in 64ths and mm on the other side.