A pillow block bearing (or plummer block) is a mounting used to support a rotating shaft with the use of bearings and various accessories. The assembly consists of a mounting block which houses a bearing.^[1] The block is mounted to a foundation, and a shaft is inserted, allowing the inner part of the bearing/shaft to rotate.^[1] The inside of the bearing is typically 0.025 millimetres (0.001 in) larger diameter than the shaft to ensure a tight fit.^[2] Set screws, locking collars, or set collars are commonly used to secure the shaft.^[2] Housing material for a pillow block is typically made of cast iron^[1] or cast steel.