How to tell the difference between 1/8 NPT and 1/8 BSPP fittings ?

[7624452]

I have a lot of fittings that I have accumulated over the years.  How can I tell the difference between NPT and BSPP, both male & female ?

[JoeShmoe]

"BSPT (British Standard Pipe Thread) is similar to NPT except there are important differences. The angle across the flanks of threads (if you sliced the fitting in half long-ways and measured the angle from root to crest to root) is 55 degrees instead of 60 degrees as it is for NPT."

I can only assume you're confusing the two Pipe Thread standards, NPT and BSPT, because BSPP stands for British Standard Parallel Pipe. The threads on a BSPP connector are cut into a cylindrical fitting, whereas the two Pipe Thread standards are on cone sections (or they're tapered, if you will).

https://www.ralstoninst.com/news/story/the-difference-between-npt-bspp-and-bspt-seals

Anyway, just lay the male fittings onto each other until you can tell that the thread angles don't match. The pointer thread is BSPT. I don't know how you would ID female connections, without extremely good eyesight to tell if the threads are rounded off or flat topped. Well, you could always get a gauge, but is that really worth it?

http://wavelen.com/blog/wp-content/uploads/2018/03/2018-03-15_14-38-11.jpg

[JoeShmoe]

Also, I wouldn't really trust an ID done by looking at if the threads were flat or round anyway, a used fitting is going to have at least some wear on it that's going to make that kind of ID more difficult.

[limbshaker]

Also the thread PITCH is different, in an 1/8 inch or -2 size,  NPT is 27tpi while BSPP and BSPT is 28tpi

Sometimes pieces and fittings are simply labeled "BSP". They don't specify whether it's tapered or parallel.

Parallel always uses a washer or dowdy seal for sealing, while taper uses sealant or tape as NPT does.

[Madd Hatter]

So what are the Chinese using for pipe thread fittings?

[mikeyb]

Metric M10x1mm pipe thread? 

I just went through this pain in the "airs" problem with my high pressure hand pump. I have many British parallel pipe threaded fittings along with a selection of NPT tapered threaded fittings, but NONE fit my hand pump ports or hose-whip. Had to order a set of metric pipe thread fittings M10 x 1mm from China. Sneaky Amazon listing that seemed to be from a seller in the US. At checkout the delivery dates were WAY out so that's when I knew parts were coming from mainland China. I couldn't find any reasonably priced parts closer, so the 4-8 week delivery time would just have to be acceptable.

Parts finally did arrive and were a perfect fit.

fmi... https://trimantec.com/blogs/t/thread-identification-guide