Starrett 10H-6-4R Cast Iron Square Head Student Combination Square, 4R Graduation, 6" Size A rugged, cast iron square head that will outlast cheap plastic and die-cast imitations An accurate, hardened and tempered square blade offered Reversible lock bolt allows the blade to be turned over or end-for-end so that all four graduated edges may be used Graduation: No. 4R - 1/8", 1/16", quick reading 1/32", 1/64"