This is called a threaded nipple. It goes on the inside of the tub and connects the faucet to the water.
There are two types of parts that can do the job and for us the wrong one shipped.
It was a funny call between me and the plumber as he explained what I needed to get.
We had to get one pronto because we had to have the part before the walls around the tub could be tiled.
Who names these things?
Anyway, here’s a threaded nipple. That sounds like it hurts.