I'm installing a freestanding tub faucet. According to the manufacturer's spec sheet the supply lines have 1/2 inch female NPSM threads, which I believe is a straight thread. I'm trying to attach these to 1/2 inch PEX-B. All of the male thread PEX fittings that I can find have MIP or MNPT threads, which I believe is a tapered thread.

Will the male MIP or MNPT be able to screw securely into a female NPSM? If not, then where would I find a fitting that would allow me to make this connection? Thank you.

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  • Have the fittings got a gasket/washer in them?
    – Ecnerwal
    Commented Jun 10, 2022 at 22:51
  • @Ecnerwal Yes, there appears to be a gasket in them. I've added a photo. Thank you :)
    – balexand
    Commented Jun 11, 2022 at 3:46
  • Those look like self sealing fittings without the proper mate they may not allow any flow.
    – Ed Beal
    Commented Jun 11, 2022 at 22:56

1 Answer 1


Since you have the gasket required to make the seal, this marriage of star-crossed lovers should work out fine.

  • Thanks, indeed it worked perfectly with the 1/2 inch MIP fitting.
    – balexand
    Commented Jun 27, 2022 at 17:45

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