Converting NPT Fittings to Fit BSPT Threading

Jun 04, 2023

We recently ran into an issue where we got our hands on a tool system that isn't widely available here in the US, so all the connections were based on European standards. Don't get me wrong, the Europeans do many things very well, like the completely rational base 10 metric system. As Americans, it seems we don't ever get away from our rebellious tendencies, so we do our own thing. When it came to getting Jon Bucklew's Festool Lex 3 pneumatic sander system set up, we needed some help converting NPT fittings to fit BSPT threading.

BSPT stands for British Standard Pipe Taper threading. NPT is National Pipe Threading. The difference is more than something simple like metric versus US standard measurements, though that does come into play. There's a difference in the threading design as well which is where the issue comes in. NPT thread is angled at 60 degrees while BSPT is angled at 55 degrees. This means you can actually get a BSPT male fitting to tighten down to an NPT female. The problem – they won't seal.

The issue we ran into with our sanders was the entire system was set up with European-sized couplers and plugs. Those sizes didn't play well with our traditional American fittings. The hose connection was somewhere in between our 1/4 inch and 3/8 inch coupler. Since 1/4 inch was too tight and 3/8 inch wouldn't seal, we needed to switch out the included fittings with American ones. That was no problem whatsoever. A quick trip to the hardware store and that step was complete.

Those new fittings were all threaded NPT and our female connections into the Festool CT 36 Dust Extractor were all threaded for BSPT – so they wouldn't seal. Back to the hardware store for adapters… this should be easy, right?

Easy to do, yes. Easy to find, not even close. It took visits to four stores to finally get pointed in the right direction. I would have never guessed who I needed to see for my air problem: the local hydraulics supply store.

It turns out that the hydraulics sector lives and dies by the BSPT system, so they had all the adapters I needed on hand. Of course, you can find the adapters online from a variety of places, but it's incredibly helpful to have a brick-and-mortar store to make sure you have everything you need and that it all fits correctly.

So hydraulics supply is the key that makes it all work. Converting NPT Fittings to Fit BSPT Threading is just as easy as adapting any other combination of plugs, couplers, and other fittings. You just have to know where to look for the adapters!