DIYbanter - View Single Post - Thread chaser for rusty drain-pipe cleaning hole?

Matt[_7_]

wrote:
Matt wrote:
If the hole is not 60mm, what size other than 60mm would be about 60mm?

A 2" NPT pipe thread is approximately 60mm in diameter.

See, the NOMINAL diameter of the inside of a 2" iron pipe is 2". The
wall thickness is approximately 3/16" thick. 60mm is approximately
2-3/8". You do the math.

You say the new plug is plastic?

Yes, and so is the old one.

You won't hurt the cast threads a bit
if with a plastic plug if you happen to cross-thread it. The plastic
threads will simply strip out.

Right, well, I can't get the new plug to stay in. I get the threads to
barely engage, but the plug pops out when I turn it. Then I look at the
threads and see that they are deformed. Isn't this explained by rust
filling the threads of the drain hole?

I'll bet if you compare the two plugs closely you will see they aren't
quite the same...

I don't much want to take the plug out just to check. My explanation of
the old plug going in easily and the new one going in hard is that the
plastic threads of the old one are deformed (somehow crushed and/or
shaved) so as to conform to the rust-reduced size of the threads in the
drain hole. It seems basically that the end threads of the old plug are
smaller than the other threads, as if the plug is tapered more. The new
plug is not so deformed and the threads are too big to go in.

I come back to the question of whether there is some size close to 2
3/8" that isn't 2 3/8". I don't believe anymore that there is such a
thing as a 60mm nominal plug.

In what way(s) do you think the old and new plugs might differ---I mean
how might they have differed when they were both new?