Jack, We keep trying to help with small details. I measured both ends of Thunder Tiger Pro .40 carburetor and there is a couple of thousandths difference. The end that belongs in the crankcase is the larger diameter, so it should be a little snugger when properly assembled. Also, note that it appears that the "O" ring is missing that goes between the carburetor and the crankcase. Any black auto parts store, or Ace Hardware store "O" ring should work. Good luck, Greg