Complete Bicycle Chain Maintenance KitIncludes 12pieces (4 pairs) professional-grade bike chain links in compact storage case. Organized packaging prevents loss while cycling, keeping essential bicycle chain link repair components accessible during trailside emergenciesTool-Free Bike Chain Link Installation SystemUser-friendly bicycle missing links feature snap-lock mechanism allowing 3-second chain assembly/disassembly. Reusable bike chain connector links eliminate specialized tools - simply align, click, and ride with confidenceSize: each missing chain link size is 21 x 8 x 10 mm; The bike chain link is 21 mm in length, 8 mm in width and 10 mm in height;Military-Grade Stainless Steel Bike Chain Connector LinkForged from corrosion-resistant stainless steel, these bicycle chain links withstand extreme riding conditions. Reinforced pin joints prevent deformation during high-torque pedaling, delivering long-lasting bicycle chain link repair performanceCompatible with: because single/1 speed chain of bike width is 21 mm, so this missing link chain is compatible to all single/1 speed chain