I have a Harbor Freight 9x20 lathe and want to change the set up on the A gear stack. This is the first time that I've tried to do that. The current A gear stack is a 28 T / 40 T on a keyed bushing shown on the left in the picture. I want to remove the 28 T gear and replace it with a 30 T shown on the right. The stack then goes on the shaft in the back and is held on with a collar with a set screw. Obviously, I want to avoid damaging the existing parts.