I use these and drill them myself. The one one lines up with the 9 hole bolt pattern.
BMX Accessories - Solid Chrome 36T Sprocket, bike sprocket, bicycle sprocket, bike chain ring | BikeWorldUSA | Bicycle Parts and Bike Accessories
Red, Those are just chainrings, they are awfully thin for a motor drive sprocket. Do they seem to hold up o.k.? I would think there would be alot of side movement with the 415 or #41 chain.
John
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