The explanation is actually straightforward. There are two main pipe threads used for vacuum components worldwide.
The first is “NPT“, which is a tapered pipe thread used in the USA and regulated per the American National Standard Institute (ANSI B2.1-1968).
The second is “G“, which is a straight pipe thread also known in the trade as BSPP, NPS or “G“, commonly used in Europe, Asia and most of the rest of the world. It is technically a Witworth thread which is actually a British Standard Pipe Parallel (BSPP) thread known as “G”. Per the ISO standard, the proper designation is “G” in front of the fraction.
This all sounds more complicated than it is; there are basically two major pipe thread types used for these pipe fittings and many combinations work together. ANVER often builds both the tapered NPT or straight “G” thread versions or uses adapter fittings to go between them. Confusion exists because many sizes of G male fittings thread into NPT female fittings without adapters even though they will not seal correctly. Here are some metric screw and pipe combinations that demonstrate this:
1. M5 and 10/32″ Male fittings thread into a M5 Female equally well. However, an M5 Male will not thread into a 10/32″ Female.
2. G 1/8″ and 1/8″ NPT Male fittings thread into a 1/8″ NPT Female though only the NPT to NPT combination actually seals tight. Even though G males can thread into a NPT female, they will almost certainly leak. A 1/8″ NPT Male will not thread into a G 1/8″ Female at all.
The 1/4″ and 3/8″ combinations do not work like this but 1/2″ and 3/4″ work marginally sometimes as they have the same threads per inch. In general BSPT (Tapered) / BSPP (Parallel) threads have different angles (55 vs 60), shapes (rounded vs flattened valleys and peaks) and in most cases threads per inch than NPT.
If you would like to know if the fittings you have selected are compatible, feel free to contact the factory. For a more technical explanation contact www.industrialpress.com for a copy of the 2700 + page “Machinery’s Handbook” which is the bible for these specifications. The above information is a layman’s explanation. If you have any comments, corrections or additions please e-mail us at firstname.lastname@example.org. Any input in making this subject clear to everyone is appreciated. Thanks!
|Pipe Size||Pipe OD||Threads Per Inch (Pitch)|| Some BSPP Male thread into Female NPT ;|
However, they Leak and are Not Recommended
|0.405″||27||28||Male BSPP “G” screws into Female NPT but leaks|
|0.540″||18||19||Does not screw in at all|
|0.675″||18||19||Does not screw in at all|
|0.840″||14||14||Male BSPP “G” screws into Female NPT but leaks|
|1.050″||14||14||Male BSPP “G” screws into Female NPT but leaks|
|1.315″||11 1/2||11||Does not screw in at all|