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, 1-3/8 in Bore Dia, 6.986 in Outside Dia, #120 Chain, 13 Teeth, 1-1/2 in Pitch, 6.268 in, 4.563 in Hub Dia, 2-1/4 in Length Through Bore, Steel