I bought these domes brand new and were cut specifically for my bike, I put the engine together, never even put it in the frame and decided to go another route. The domes are brand new and never used. They are cut for bore 64mm to 66mm bore, so the o ring goes on the outside edge of the domes. (You can see in picture) They are 23cc and are for, a 4 mil longrod with blaster pistons.(no space plate) They were cut originally to run 92 octane at 0 altitude with a dune port by HJR, and I was using 66mm blaster pistons. I'm looking to get 65 dollars for them shipped obo. I can take more pics if needed. Bought for 80 brand new and you get them brand new for 65 shipped to your door. If you have any questions feel free to ask.