"Timing belts", "toothed belts", "cogged" or "cog belts", and "synchronous belts" are non-slipping mechanical drive belts. They are made as flexible belts with teeth moulded onto their inner surface. The belts run over matching toothed pulleys or sprockets. When correctly tensioned, these type of belts have no slippage, and are often used to transfer motion for indexing or timing purposes (hence their name). They are often used in lieu of chains or gears, so there is less noise and a lubrication bath is not necessary.