On Jul 21, 11:16*am, Limp Arbor wrote:
I need to add a trap to my cast iron drain in my basement.

I'm going to remove my 4" cleanout and run the trap into that fitting.

Here's the difficulty:
My cleanout plug is threaded into a bushing held into the bell end of
a cast fitting. *The threaded cleanout is a little shy of 4" (about 3
15/16) *I bought a 4" threaded male PVC fitting but it is about 4 1/4.

Do they make a threaded PVC fitting that will go into a 4" female
steel?

Should I just remove the bushing and get the rubber boot that will let
me go from the bell end of the cast down to 4" PVC?

Very strange. AFAIK, all pipe fittings are based on inside diameter.
So the 4" PVC you have should go into the 4" cleanout threads.
Given that you say it misses by about 5/16 or so, I can't imagine
what you have. The Fernco type rubber coupling is probably
your solution.