Metal idler sprockets sprockets maintain proper chain pressure, and instruction the chain around obstacles and stop excessive chain use and vibration. You don’t need any special tightener shafts for ball bearing idler sprockets. Composite sprocket idlers need no lubrication and so are corrosion resistant and wear-resistant.
An idler sprocket is a gadget used to maintain the tension in a chain or chain drive system. Often consisting of only a sprocket installed on a spring tensioned arm, the idler sprocket pulls against the chain in a constant manner to keep the chain tight at all times. How big is the sprocket used in an idler sprocket assembly has no effect on the performance of the chain drive; however; a larger sprocket will often go longer because of the slower rate of the sprocket, which saves use on the sprocket’s bearings. Maintenance for the idler assembly is commonly no more than an occasional greasing of the sprocket’s bearings.
When traveling a machine by chain, the tension of the chain must be kept at a constant to avoid the chain coming off of the drive sprockets. By setting up an idler sprocket in the drive program, the chain is kept taut without being over-tightened. Working a chain within an over-restricted condition can result in premature bearing and chain failure while an idler sprocket placed in the program is usually a way to significantly extend the life of the chain, sprockets and the bearings on the machine’s sprocket shafts.
The ideal installation of the idler sprocket is on the opposite side of the chain between your drive sprocket and the driven sprocket. The application should place the idler sprocket in a position that has the sprocket pushing or pulling the chain towards itself as it loops the two main sprockets in a form like the letter B. This design will allow the pulleys to draw the chain hard without hindering the idler in any way as the drive chain passes over the sprocket. If a condition occurs which requires the drive to exert extra pressure on the drive chain, the idler will flex against the chain, and can expand while remaining in contact with the drive sprockets.
While the vast majority of idler sprockets are manufactured of steel, many materials are used to produce an idler sprocket. Many poly or composite sprockets have been used with great success plus some wooden sprockets are also applied to some machinery without issue. Many machines, in an attempt to reduce the put on on the drive chain, use an 
aluminium, cast iron or metal sprocket coated in a nylon material. The metallic hub enables the idler sprocket to stay very strong while the nylon covering is definitely soft on the chain links.