Shimano Alfine CT-S500 Chain Tensioner Allows the use of an internally geared hub on a frame with vertical drop-outs. Chain Tensioner 20 tooth max rear sprocket 16 tooth chainwrap capacity 41.8mm chainline Uses washers on on the mounting bolt for 5mm of chainline adjustability Compatible chain - 3/32" | Shimano Alfine CT-S500 Chain Tensioner Black, 20T Max, Single Speed