Knowing what fittings we're dealing with will go a long way in keeping us all safe! Bookmark this thread so, you can refer to it when you need to. And, please toss me some accuracy if you think this is helpful. 
I got this article from Ralston Instruments. It is the best representation and explanation I have found.
Air gunners and Paintballers generally use ~1/8" sized fittings. We may upsize to 1/4" and back down again, but our primary fittings are ~1/8". I found out that there are actually 5 types of fittings in this size category! The vast majority of us will use either NPT, BSPP, or BSPT. Even BSPT is pretty rare.
Connecting a NPT to a BSPP is not safe. You might be able to get it to work and think everything is fine. But, you are leaving yourself open to failure and possible injury. The best case scenario is that you'll only lose air at higher pressures. But, why leave yourself open to any of that? Generally, these fittings are pretty inexpensive and the shipping ends up costing more than the part (unless you're talking stainless steel). Another hazard to using the wrong fitting is when you're forcing this and one of your pieces is made out of aluminum. This can put a tremendous amount of strain on the tiny threads and possibly strip them right out. Then you'll have an expensive repair on your hands.
I found some NPT to BSPP and vice versa on eBay. I also found some steel as well as stainless steel fittings at a hydraulic supply company. My favorite place to shop for high pressure fittings is Northshorecompressor.com. However, they don't seem to carry any BSPP stuff.
I would also suggest spending the extra $ for stainless steel vs steel fittings. They are made much cleaner and more precise and generally look better as well.
-BTW, "BSPP" is sometimes abbreviated as just "BSP"-
Always remember to double check your fittings pressure ratings before ordering!
My suggestion, get converter fittings from this to that, and that to this. Have them labeled and stashed in a drawer so that when you run into that situation where you need this to go into that, you can make it happen and get on with your project.
I hope you find this info useful and educational. Stay safe and, Happy Shooting!
Tom
I got this article from Ralston Instruments. It is the best representation and explanation I have found.
Air gunners and Paintballers generally use ~1/8" sized fittings. We may upsize to 1/4" and back down again, but our primary fittings are ~1/8". I found out that there are actually 5 types of fittings in this size category! The vast majority of us will use either NPT, BSPP, or BSPT. Even BSPT is pretty rare.
Connecting a NPT to a BSPP is not safe. You might be able to get it to work and think everything is fine. But, you are leaving yourself open to failure and possible injury. The best case scenario is that you'll only lose air at higher pressures. But, why leave yourself open to any of that? Generally, these fittings are pretty inexpensive and the shipping ends up costing more than the part (unless you're talking stainless steel). Another hazard to using the wrong fitting is when you're forcing this and one of your pieces is made out of aluminum. This can put a tremendous amount of strain on the tiny threads and possibly strip them right out. Then you'll have an expensive repair on your hands.
I found some NPT to BSPP and vice versa on eBay. I also found some steel as well as stainless steel fittings at a hydraulic supply company. My favorite place to shop for high pressure fittings is Northshorecompressor.com. However, they don't seem to carry any BSPP stuff.
I would also suggest spending the extra $ for stainless steel vs steel fittings. They are made much cleaner and more precise and generally look better as well.
-BTW, "BSPP" is sometimes abbreviated as just "BSP"-
Always remember to double check your fittings pressure ratings before ordering!
My suggestion, get converter fittings from this to that, and that to this. Have them labeled and stashed in a drawer so that when you run into that situation where you need this to go into that, you can make it happen and get on with your project.
I hope you find this info useful and educational. Stay safe and, Happy Shooting!
Tom
