Inside spring calipers are used for measuring and transferring precise inside (ID) measurements. These are a well-made pair of inside calipers for an excellent price. These dividers are made from high-grade carbon steel with hardened, rounded and finely polished points. They feature a rapid-adjust quick-spring nut for rapid and precise fine adjustments that will securely hold any measurement. To make large adjustments, tip the nut to disengage the threads, and slide to a new measurement. Release the nut to engage the threads and turn for fine adjustments. The adjustment mechanism is central located to assure smooth action. Fulcrum and adjustment mechanism are brass. “Yankee” style flat-leg construction makes these units very durable. They have a substantially hardened spring for years of service. Size 12 inch, Max opening 12.5 inch