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Adding threads to 3/8" iron pipe

Have a small leak in the bathroom and I need advice on. Just refinished the bathroom so ripping out and replacing all the pipe is not an option

We have old 3/8" iron pipe supply lines throughout the house.

The leak it where iron pipe meets the shutoff valve and I still can't manager to nip it.

The old iron pipe has a rusty connection end with bad threads. No amount of Teflon tape, plumbers putty, plumbers epoxy, O-rings, or similar seems to help.

My next plan of attack is to just add more threading onto the existing pipe, then cut off the bad section. (I have 6-8 inches of pipe to work with on the finished side of the wall)

However I can't seem to find a proper die set to actually add more threads.

The true O.D. of a 3/8 Iron Pipe is .675 inches which is not a standard die size.

Would using a 5/8 die be detrimental? .625" vs .675" so .05 inches difference - should both be 18 threads per inch...

Any Advice?

Re: Adding threads to 3/8" iron pipe

We commonly see 1/2" galvanized iron pipes and nipples, not 3/8".

But whatever size nipple you have coming out the wall, try to unscrew it, using a plumber's wrench. The bigger the wrench, the better, subject to space available. Use some force, but be careful not to bend it. Be patient.

Once you have the nipple out, take it to a place where they have a threading machine available, or just replace it.

Re: Adding threads to 3/8" iron pipe

You need a standard 3/8"-18 NPT pipe die.


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