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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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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 '20 at 21:58

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