Power transmission belts, sometimes called drive belts, gear belts, or automotive belts, transmit power between two components, such as from a motor or driver to a drive shaft or pulley. Round belts are used on serpentine drives, line shaft conveyors, and commercial sewing machines. Connectors are used to connect two ends of a round belt that has been cut to size or needs to be installed without disassembling the drive system. Twisted O-rings are installed in V-belt and round belt pulleys and have a hook connector so they can be installed without dismantling the drive system. Variable-speed belts are used with variable-speed pulleys and accommodate changes in speed and pulley width as the drive systems speeds up and slows down. Belt accessories protect, maintain, and measure belt grooves and tension.