Starrett 73 Series "Yankee" Spring-Type Inside Calipers with Flat Legs and Quick-Spring 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 6". 6" (150mm) with Quick-Spring Nut Caliper size and capacity is 6".