Power transmission belts, also known as drive belts, gear belts, or automotive belts, transfer energy from one component to another, such as a motor or driver to a drive shaft or pulley. Serpentine drives, line shaft conveyors, and commercial sewing machines all employ round belts. Connectors are used to join two ends of a cut-to-size round belt that needs to be inserted without disassembling the drive system. Twisted O-rings with a hook connector are inserted in V-belt and round belt pulleys and can be installed without disassembling the drive system. Variable-speed belts are used in conjunction with variable-speed pulleys to allow changes in speed and pulley width when the drive system accelerates and decelerates. Belt accessories keep belt grooves and tension in good shape by protecting, maintaining, and measuring them.