Inside spring calipers are used for measuring and transferring precise inside (ID) measurements. These calipers are made from high-grade carbon steel with hardened, rounded and finely polished points. They feature a solid nut for precise fine adjustments that will securely hold any measurement. Adjustment mechanism is central located to assure smooth action. “Yankee” style flat-leg construction makes unit very durable. They have a substantially hardened spring for years of service. Maximum opening is 12 inches or 300 mm.