V-belt pulleys or sheaves mate with drive belts in numerous power transmission applications. V-belts are efficient, cost-effective, and designed for non-critical ratio drives. They usually have a triangular or trapezoidal cross-section and are reinforced with fiberglass, polyester, or steel. V-belt pulleys are made from materials such as aluminum, brass, cast iron, steel, stainless steel, plastic, or zinc alloy. Both single groove and multiple groove devices are commonly available. There are several basic types of products. Standard V-belt pulleys have one or more grooves and are designed for general-purpose applications. Variable speed pulleys have faces or flanges that adjust axially to vary pitch diameter. Idler pulleys are used as belt tensioners and contain bearings that allow free rotation. Companion pulleys have ribbed webs for high strength-to-weight ratios. Multiple-size pulleys use step-down or cone configurations. Poly-V pulleys are used with mating belts for high-speed power transmission. Typically, both the section designation (H, J, L, M, or PK) and the number of ribs requires specification and belt-pulley matching.