Spring-Tempered Steel Rule, Millimeter and Inch Figures, 0 to 150mm/0 to 6" Length. The Starrett C636ME-150W/SLC, 150mm - 6" Spring-Tempered Steel Rule with Millimeter and Inch Graduation includes graduations at 32nds and 1/2mm on One Side; 64ths and mm on Reverse, with standard letter of certification.