I was trying to fix up an old bike of mine and was trying to figure out the BCD (Bolt Circle Diameter) of my cranks. I came across a helpful resource, Sheldon Brown's 5-Bolt Chain Wheel Guide, and I was able to find the right BCD for my cranks. I used an M5x 25 bolt to attach the middle cylinder to the guide, but it can still be used without the middle cylinder attachment.