Roller Chain Sprocket Bore Diameter 25 mm For Chain Pitch 1/2 in For Number of Strands Single Hub Type One Side Material Steel Maximum Bore Diameter 25 mm Number of Teeth 21 Outside Diameter 3.7 in Pitch Diameter 85.21 mm Bore Type Fixed Chain Number 08B Finish Black Oxide Hub Diameter 70 mm Hub Projection 0.812 in Includes Set Screws Keyway Yes Keyway Width 8 mm Length through Bore 28 mm Number of Set Screws 2