So I've got this buyang 110cc quad and the gas cap is gone. I've looked online for one but from what I can tell they don't exist. The opening on the tank is 50.8mm. My question is am I to measure just the I.D. of the tank opening or thread to thread? I'm struggling trying to find one that appears to fit. I've also looked for just a whole tank but nothing really matches up to what I have.