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I'm researching paint guns and came across the DeVilbiss 802342 kit. I noticed though that it has 1/4" NPS threads, even though I've only ever seen NPT used for air plugs. A quick search indicates that these types of threads will engage, but won't seal properly. No sources seem to say whether or not this can be fixed with thread tape/dope, only that thread tape/dope is required for NPT connections. One other source I found said that generally NPT is used for air connections and NPS for fluid connections, although the DeVilbiss website specifies that this is for the air connection.

Looking at various websites, I can't find a 1/4" NPS air plug anywhere, even McMaster-Carr. I've never paid much attention to the fittings on my air tools, just checked whether they were male or female threaded and put a 1/4" NPT plug on there. Is it common for air tools to have NPS threads on the tools themselves? Will a NPT plug work with NPS threads (assuming proper thread sealant is used)?

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  • There's nothing like the "Right Stuff" to seal things up ... – Pᴀᴜʟsᴛᴇʀ2 Feb 12 at 2:28
  • More searching has only uncovered a single forum post and another article saying, "you pretty much never see NPS on air tools so you don't have to worry about it." Reminds me of this xkcd. – zaen Feb 12 at 3:24
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I was able to find the answer, finally.

To the question of whether or not NPS threads are common on air tools, the answer is they appear to be uncommon on everything but paint sprayers. However, the only NPS fitting I've been able to find after a couple of hours of intermittent searching I've only found a single NPS fitting, made by the DeVilbiss.

DeVilbiss makes a line of proprietary "high-flow" fittings that don't appear to be compatible with normal air hose fittings, so they require buying both a plug and a socket. While the majority of these are NPT, they make a single model of NPS female threaded plugs specifically for their spray guns. Annoyingly, that means buying a dedicated hose for the paint gun too, since the rest of my (and I would assume almost everyone's) air system doesn't use proprietary DeVilbiss fittings.

One user on Amazon reports that he's used "a standard air fitting," presumably NPT, in place of one of these for years without a problem. As non-authoritative as that source is, it's the only information I've been able to find.

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  • Actually, I'm noticing that Harbor Freight paint guns also use NPS. If I come across any others I may have to amend the statement about NPS being uncommon. This does seem to indicate that NPT plugs work with NPS tools though, since HF doesn't sell NPS plugs and I doubt many people are buying $35 worth of connectors for a $16 tool. – zaen Feb 12 at 4:16

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