500mm - 19-1/2" Spring-Tempered Steel Rule - Millimeter and Inch Graduations, Graduations at 32nds & 1/2mm on One Side; 64ths & mm on Reverse. The Starrett 500mm - 19-1/2" Spring-Tempered Steel Rule with Millimeter and Inch Graduation features a satin chrome finish. Graduations at 32nds and 1/2mm on one side; 64ths and mm on reverse. 500mm (19 1/2"), No. 36 Grad.