On Jul 21, 8:16*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?

How about some photos?

Pipe, having a "nominal size" that often bears little relationship to
its actual dimensions, is typically controlled by th OD.

That is, most 4" pipe has the same OD.
Threaded pipe elements (PVC, brass, steel, stainless) will all fit
together independent of wall thickness.
(pipe schedule) because the pipe gets thicker by reducing the ID.

As odd as it may sound your threaded plug might be 3-1/2"

http://www.grainger.com/Grainger/OAT...&cm_vc=IDPRRZ1

Unfortunately cast iron pipe defines this standard because it was
never meant to be assembled by threaded joists.
Lead & okum(?) was used years ago and now no-hub coupling.



Without a photo its hard to tell what you've got but if no hub
coupling should let you do whatever you need to do.

One warning, if the rest of the drain system above this point it cast
iron, the section you cut our might be supporting the piping above.
Secure the pipes above the cut by blocking well at an old bell joint.

cheers
Bob