72 Tooth Sprocket - 4-1/2" Drum for 35 Chain. Use with internal drum brake. Mounts to Azusa Tristar wheels. The three bolt patterns are as follows:3 holes (5/16") on a 3.75" Bolt Circle4 holes (1/4") on a 3.75" Bolt Circle4 holes (1/4") on on a 3.228" Bolt Circle (these holes are a bit differently spaced to accommodate the four holes on the mini-hubs AZ_2561 / AZ_2568 / AZ_2565)