I have this compressor valve which dates from 2009. It got screwed on too hard and finally split. I'm looking to replace it either by another such valve or just an adapter to 1/4" NPT. I'm just unable to figure out the threading standard of the female side (non-NPT). I took some measurements and compared with a variety of standards. None of them comes close enough to be a match.

I've got the following measurements:

  • Internal diameter seems to be about (or slightly more than) either 1/2" or 13 mm. Don't think it's tapered, but I might be wrong. Since it's split and I don't have the counterpart (helping my uncle find a replacement), it's a bit hard to tell.
  • Using thread pitch gauges, the best matches I get are either 27 TPI or 1 mm.

It's not significantly closer to imperial or metric to help me guess which it might be.

It's like a hybrid of BSP 1/8" for the threading and BSP 1/4" for the diameter. That's the best I can tell, which isn't useful to find a replacement.

EDIT 2024-06-11: I might have found what that thread is. Can't fully confirm, but that looks a lot like BSB 1/2" (British Standard Brass). That's an interesting standard where the thread pitch stays constant regardless of the diameter of the pipe, reducing stress on the pipe wall to save brass on larger pipes.

My uncle went around the city to every hardware store and to the more industrial shops that might have such rarer parts for sale: shrugs all around or suggestions to use NPT.

I've communicated with King Canada, which is the maker of this compressor (model 8489). They've replied with a shrug. It would be the part #88 in the service manual.

A couple pics for a visual:

Side view of the damaged valve Female end view (mystery thread) of the damaged valve

  • +1 for documentation. Possible, if sloppy, work-around: use a piece of high-pressure hose and strong hose clamps to connect to a shut-off valve with two male fittings. Yes, a definite likely point of failure. Commented Jun 10 at 22:33
  • Should be able to match/find a replacement at a plumbing or hardware store. Automotive/tractor supply store also.
    – crip659
    Commented Jun 10 at 22:33
  • @crip659 I should have mentioned that. We went where the compressor was bought, and then to every place in the city, including less known / more industrial shops where they might have such parts. Shrugs all over, or very confident that NPT will do. Obviously NPT doesn't fit there at all. I'll likely still ask around until I get the answer. Hard to believe it would be a thread invented only for this junction.
    – Joanis
    Commented Jun 10 at 22:42
  • @DrMoishePippik I'm definitely looking for a proper fix first. Would rather avoid flying compressor fittings in the garage. I suppose if we really can't find anything, we'll think about soldering or removing more parts to rebuild the assembly with more current pipe threading standards.
    – Joanis
    Commented Jun 10 at 22:48
  • I also doubt king would use fittings only from them. The threaded end looks like common NPT thread. There are a few different quick connect fitting types, so might need to change both ends of quick connect.
    – crip659
    Commented Jun 10 at 23:01

1 Answer 1


That mystery thread is not a customer facing feature. it's from the manufacture of the valve. and the valve has now split into two pieces. The missing part of the valve would have the ball seat for the open end.

In the picture it shows the valve should be male on both ends. and it probably has the same thread both ends

enter image description here

This also explains why many of the experts you talked to said that a regular quarter-inch valve is what you need.

  • That makes a lot of sense. Wow, I didn't see it that way. I bet there's still the other half of that valve on there. I'm gonna try to get a confirmation on that. Thanks! I'll ✅︎ as soon as confirmed.
    – Joanis
    Commented Jun 11 at 6:42

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