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I realize that there must be some sort of o-ring, gasket, or washer, but from an engineering standpoint it is not clear how to know what fitting will seal to what without having the parts in front of you and experimenting.

Most plumbed components from outside the US come in this standard, but there are never any o-rings provided or recommended. Surely there must be some specifications for each type and their respective pressure ratings.

  • This pipe thread comparison article indicates using a copper crush washer at the male face.
  • Wiki shows a fitting with a rubber o-ring at the root of the male threads.
  • ISO 228 exists, but like all these standards to have to buy it.
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  • $\begingroup$ Accepting an answer is good practice.. $\endgroup$
    – Solar Mike
    Sep 27, 2023 at 5:49

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BSPPs requires gaskets. They're great. I find them so much more reliable than tapered threads. I could not get my vacuum system to acceptably seal work with any tapered threads be it BSPT, NPT, NPTF or otherwise. But BSPP did the trick with gaskets. Also less fussy to machine the holes they go into.

Some BSPP fittings I have bought do come with gaskets. Others I need to buy the gasket separately but they do exist. They are a more of a sealing washer (the metal-rubber concentric ring type, not the rubber-metal stacked type) than a gasket and are specifically made for BSPP of different sizes. May also be referred to as an O-ring in some cases but you want the metal-ringed rubber. The washer part prevents the rubber part from splaying out when you tighten the thread.

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  • $\begingroup$ I agree, that they are much better than taper threads for sealing. The downside is that there does not appear to be any clear publicly available terminology to properly specify and order parts from different vendors and have them be compatible. If you come across some terminology for the different types of seals and how they work between different vendors please let me know! $\endgroup$
    – ericnutsch
    Sep 27, 2023 at 8:55
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    $\begingroup$ @ericnutsch On McMaster-Carr they are literally called "O-Rings for Brass Compression Tube Fittings". You can ask them for manufacturer part info which may give more general info. I think they you may be able to jut specify rubber bonded sealing washers of particular dimensions. $\endgroup$
    – DKNguyen
    Sep 27, 2023 at 15:43
  • $\begingroup$ @ericnutsch mcmaster.com/products/tube-fittings/… $\endgroup$
    – DKNguyen
    Sep 27, 2023 at 18:37
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What I read in the references is BSPT is tapered similar to NPS. Of course you still need pipe dope to fill the spiral leak path, so not good for very high pressures such as 1000 + psi. The BSPP requires a copper washer, known as a metal to metal seal in the trade. There are hundreds of patented tubular threads used for oil/gas well pipe with various sealing techniques but I don't remember a metal to metal like BSPP . As a non-expert my guess is that is is not a very good system for very high pressures. But I have to accept that it is widely used outside North America.

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  • $\begingroup$ Yeah BSPT makes sense. I usually only need up to 200psi pressure, but its just not clear which ones take which sealing system. I suppose most people must just pipe dope these connections same as tapered thread and cross their fingers. $\endgroup$
    – ericnutsch
    Jul 2, 2020 at 21:58
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Generally when plumbing in threaded metal pipework fitters will generously apply PTFE tape to the threads as it fills the minute gaps between the male and female threads. also search boss white and hemp.

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