Using NPT plumbing on BSPP pumps

I am looking for a replacement pump for a GX390, and am puzzled about using NPT plumbing on BSPP pumps.

The inlet and discharge ports of all pumps I’ve looked at except CAT have BSPP (British Standard Pipe Parallel) thread. Most of the plumbing available for the pumps has NPT (National Pipe Tapered) thread. The following from states not to mix BSPP and NPT threads:

“Never swap threads if it is a high pressure application.

“NPT/NPS and BSP threads are not compatible due to the differences in their thread forms, and not just the fact that most sizes have a different pitch. NPT/NPS threads have a 60° angle and have flattened peaks and valleys (Sellers thread form) where as BSP threads have a 55° angle and have rounded peaks and valleys (Whitworth thread form).”

3/8” NPT has 18 threads per inch, while 3/8” BSPP has 19 threads per inch. 1/2” and 3/4” NPT and BSPP all have 14 threads per inch.

I asked a pump retailer and two pump manufacturers about using NPT plumbing on BSPP pumps, and have received no answer.

My impression is that typically NPT plumbing is used on BSPP pumps. Please educate me about this.

I havent seen any american pumps or pumps for sale in America that have British threading. I suppose you should specify threading if you arent in America, Im quite positive theres a standard/metric rule on imports. Ask a machinist on compatibility.

Thank you for your reply.

I have verified that the inlet and discharge ports of the following direct drive pumps sold in the U.S. have BSPP (British) threads:

Udor ML 4.0/35-W (information from sales representative at UDOR USA)

Legacy GS4040G.3, see:

Annovi Reverberi RRV4G40D-F24, see:

General Pump EZ4040G, see:


I’ve got the personal phone # of 1of the general pump technical support guys if you want it to ask them.

Yes. Thank you. I don’t know the process for sending and receiving the phone number privately.

Redjess: If you want, you can email the general pump technical support guy’s phone number to me at

I sent it to you in private mssg.

Reviving this thread…

I’m putting together a 5gpm setup with an Udor BC18/20 and a ZK1 unloader, which both seem to have BSP threads, so I find myself ordering several BSP to NPT adaptors.

Im surprised there isn’t more discussion here about it. Maybe my searchers are missing it. It seems that most people just crank on the NPT fittings and call it a day, but it also seems there aren’t many people running into issues afterwards. At least they aren’t posting here about it.

Myself, I’m going to rely on the proper adaptors for these high pressure connections,

You do whatever is comfortable for you.

I’ll just say this: brass is malleable, and deforms to a degree when you make an NPT-NPT connection. It deforms just a little bit more when you make an NPT-BSPP connection. In real life use, there’s no difference in serviceability.

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Servicability is my primary concern, assuming it is safe to ignore BSP/NPT compatibility. I wouldnt want to damage my pump and then require a new head. Although I guess replacing only the head wouldn’t be the end of the world anyway.

If the head is steel and the fittings used are brass (my plan), it seems unlikely that i would damage the head anyway. Maybe ill go ahead and try without the additional cost of the adaptor fittings. It seems that most do just that.

Edit: the manifold is brass.