B style sprockets are flat sprockets with a hub extension on one side. These plain bore sprockets can easily be bored to a metric or standard size to fit your application. Keyways, set screws and hardened teeth are quick alterations that can be made. Martin Single Pitch Roller Chain Sprocket, Stock Bore Type B, 1 in Bore Dia, 3.678 in Outside Dia, #80 Chain, 10 Teeth, 1 in Pitch, 3.236 in, 2.563 in Hub Dia, 1-5/8 in Length Through Bore, Steel