Rotary shafts are elongated, rod-shaped devices that rotate about a longitudinal axis and transmit torque. They are similar in shape to linear shafts, but are designed to withstand torsional forces. Some rotary shafts have tapped or untapped axial holes for mounting to support structures. Others are grooved for the placement of snap rings or channeled for keyways. Solid or hollow rotary shafts with male or female threads and stepped or chamfered ends are also available. Rotary shafts with break edges are deburred, but not chamfered. Precision ground products are also available. Most rotary shafts are made of aluminum, alloy steel, carbon steel, stainless steel, composite materials, or plastics. Alloy steel is harder than carbon steel and provides superior durability. Stainless steel is well-suited for applications in which corrosion resistance is an important consideration. Aluminum rotary shafts provide good electrical and thermal conductivity, high reflectivity, and resistance to oxidation. Composite materials are often made of carbon fibers bonded together by resins. They are not as strong as metal shafts, but are lightweight and help reduce energy requirements.