A grooved pulley wheel, mounted on plummer blocks, at the top of the headgear. The winding rope passes from a cage or skip around the sheave and onto the winding drum. For normal loads, the sheave rim and boss are made of castiron, and the spokes are made of round, mild steel. Winding sheaves range up to about 24 ft (7.32 m) in diameter. Sheaves up to 8 ft (2.44 m) in diameter are usually made in one piece, but above this size, they are built in halves and bolted together. To give efficient service, the sheave diameter should be at least 96 times the winding rope diameter.