Starrett 73 Series "Yankee" Spring-Type Inside Calipers with Flat Legs and Solid Nut are made from a high-grade steel and well-finished. The legs are made of flat stock and are very durable. Calipers feature a hardened fulcrum stud, strong and flexible bow string, and centrally located leg adjustment to assure smooth action. Caliper size and capacity is 4". 4" (100mm) with Solid Nut assure smooth action. Caliper size and capacity is 4".