I have a soldered copper water pipes that terminate in a 3/4" male thread adapter. That is screwed into a brass gate valve female-female. The valve won't close fully.

I want to cap the pipe. I can use a pipe plug on the brass valve or remove the valve and use a pipe cap on the copper thread adapter. I don't want to un-solder the thread adapter for a sweat cap.

Shopping around, I find plugs and caps in PVC, galvanized iron or black iron. Copper threaded caps seem nonexistent and brass ones are rare and expensive.

I don't want to use solder because it involves soldering.

I don't want to use brass or copper because the stuff is expensive. Can I get away with PVC? This is all on cold pipe. What's my best choice to avoid galvanic corrosion problems?

3 Answers 3


You could cut off the threaded adapter so you have plain copper pipe, then push on a Shark-Bite cap (they're about $6-8 at most home centers or hardware stores).

Otherwise, a stainless steel cap could be used if you're having a hard time sourcing an affordable brass threaded cap.


a brass plug with thread tape should be sufficient. Removing the valve and capping the copper male fitting would also work just as well but requires turning off the water supply.

  • Do you think a PVC plug with threaded tape would work instead? It's a lot cheaper and easier to find. Aug 22, 2016 at 2:46
  • 1
    @Harper It may work in the sort term. In my experience, mixing metal and plastic threads almost never ends well.
    – Tester101
    Aug 22, 2016 at 10:28
  • Well... Iron is right out. Not the answer I was hoping for, but I sure don't want to do this job twice. Thanks. Aug 23, 2016 at 14:30
  • Harper could not find a way to contact you through a private message. I'll gladly PayPal you eight dollars so you can buy you a brass plug. m.homedepot.com/p/…
    – Alaska Man
    Aug 24, 2016 at 17:39
  • 1
    If the existing adapter had female threads, you could probably use a PVC plug. However, when male metal threads are used with female plastic fittings, the metal typically expands the plastic enough as it's threaded together to cause a leak. When you go the other way (female metal with male plastic), the metal tends to compress the plastic instead and makes an okay connection.
    – William S.
    Dec 27, 2016 at 21:23

Solder a cap on a short nipple, then solder the capped nipple into a female threaded to sweat adapter. Then thread the whole mess onto the male threaded fitting.

enter image description here

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.