I tried to replace my leaky bath tub faucet. When I removed the stem, I didn't see any stem seat. I think previous owner in my house didn't properly install stem seat.

Is there some way to identify the size of stem stem seat? I tried 7/16 inch one but it seems too small. When I tried 1/2 inch 20 thread one, it wasn't going in. Either thread is not correct or size is too big I guess.

What other sizes should I try?

Thanks.

The best bet is to remove the other side seat and then you could match it up with one at a plumbing supply. What is the brand of faucet? If it is a well known brand, you might find one at HD or Lowe's