Martin metric double strand solid construction sprockets have proper spacing between chain rows. The sprockets are manufactured from high carbon steel. Martin does not stack \"A\" plates on multiples, but instead Martin machines teeth after the chain rows are already in place. These plain bore sprockets can easily be bored to a metric or standard size to fit your application. Keyways, set screws and harden teeth are quick alterations that can be made. Martin Roller Chain Sprocket, Type B Double Strand Solid Stock Bore, 16 to 60 mm Bore, 116.197 mm OD, #10B-2 Chain, 21 Teeth, 15.875 mm Pitch, 106.513 mm Pitch Diameter, 84.988 mm Diameter Hub, 45.009 mm Length Through Bore, High Carbon Steel