The Chain Keeper is a guide to keep your chain right where it belongs. Mounted in place of a front derailleur, the Chain Keeper works with single chain ring drivetrains using a narrow chain. The chain block surrounds the chain as it meets the chain ring and prevents it from skipping off. TECHNICAL INFORMATION 6061 Aluminum Weight-69g Finish-Anodized, Anodized Color Black, Purple, Silver Clamp Size- 28.6mm, 31.8mm, or 35.0mm Chainline Range 34-55mm PRODUCT STORY The Chain Keeper clamps on to the seat tube of the frame. The portion of seat tube where the clamp mounts must have a circular profile and a diameter of 28.6, 31.8, or 35.0mm, (+/-0.5mm). Designed with adjustability in mind, the Chain Keeper can accommodate a range of chainline measurements and chain ring sizes.Note: This is not designed for downhill, freeride, or big hit use.