... . material: alloy steel 2. color : blue, black, yellow and natural B series roller chainsSpecification:1. Simplex: 04B-1, 05B-1, 06B ... -1, 48B-1, 56B-1, 64B-1,72B-1.2. Duplex: 05B-2, 06B-2, 08B-2, 10B-2, 12B-2 ... 8187 standards.Color: blue, black, yellow and natural industrial transmission chain (B series)