Metric 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 Simplex Roller Chain Sprocket, Metric Stock Bore Solid Type B, 25 to 75 mm Bore Dia, 186.296 mm Outside Dia, 16B-1 Chain, 21 Teeth, 25.4 mm Pitch, 170.421 mm, 106.782 mm Hub Dia, 50.013 mm Length Through Bore, Steel