Chain Checker: A worn chain shifts poorly and wears sprockets at an accelerated rate. 0.75% and 1%, the points at which chain experts suggest replacement. Compatible with all chains. Easy to use. Chainstay Protectors: Prevent nicks and scratches to your bike frame. Simply attached to your bike frame with two cable ties we supplied. Suitable for normal rode bike and mountain bike also. Washable, durable, and more convenient. Specification: Chain Checker: Material: Carbon Steel Total Length: Approx. 140.5mm / 55.3inch Width: Approx. 47mm / 18.5inch Chainstay Protectors: Material: rubber Color: Black Size: 220x22x25mm/ 8.66x0.87x 0.98inch Package Includes: 1 Piece Chain Checker 2 Pieces Chainstay Protectors Note: Product chain size: 0.75 means that the chain is stretched 0.75mm for every 11 knots. 1.0 means that the chain is stretched by 1mm every 11 knots.