This GT2 timing pully has 16 teeth and is designed to be an idler in a belt system. Unlike a standard GT2 pulley, this one has a set of bearings pressed into the center bore. The bearings have a center bore of 3mm and allow the pulley to spin freely on a stationary shaft or bolt. The pully is designed to work with all forms of 6mm wide GT2 belt we carry in stock.