http://www.tjondgear.com/sproc....ket/finished-bore-sp ChinaFinishedBoreSprocket A sprocket idler is a sprocket with built-in bearings. Its main functions include changing the steering of the driven wheel, tensioning the chain, and adjusting the pressure angle.The idler gear is a part of the gear train that plays a transitional role and will not change the transmission relationship. It is to make the force of the gear train more reasonable or to meet the layout of the entire transmission system. Only sprockets and chains of the same specification can be used in combination. This series is ISO standard 04C/ 06C/ 08A/ 10A/12A/16A (