? Starrett "Yankee" Calipers and Dividers are made from a high-grade steel and well-finished ? The bow spring, although flexible, is exceedingly strong to assure reliability ? All sizes are available with either spring nut or solid nut ? The Starrett quick-adjusting automatic-closing spring nut is designed for making fast, positive adjustments ? Fulcrum stud is hardened and has a smooth bearing surface ? The legs are made of flat stock and are very durable ? The threads of the nut firmly engage the screw at the slightest pressure from the leg ? When the pressure is withdrawn, the nut automatically releases itself, sliding freely over the screw