ANVER Vacuum Material Handling

  Vacuum Fitting Conversions
Standard Sizes for Threads used in the Vacuum Component Industry

It 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).
        Positives: The common thread standard in North America
        Seals tight thru the threads even though the technical books say it does not
        Does not require rubber O-Rings or washer seals

        Negatives: It is not the world standard which is Metric or “G” straight thread type
        Requires rubber O-Rings or washer seals

The second is “G” which is a straight pipe thread also known in the trade as BSPP, 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 to use “G” in front of the fraction. 

        Positives: The common thread standard in industrialized world, The way to go if you export.
        Seals tight thru O-Rings or washer seals as the technical books say it should
        It insures that all items have the same height when fully tightened

        Negatives: Not the North American standard
        Requires rubber O-Rings or washer seals

This sounds more complicated than it is as 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 adaptor fittings to go between them. It is not an exact science as many sizes of G male fittings screw into NPT female fittings perfectly without adaptors.  Here are some combinations that demonstrate this:

1. M5 and 10/32″ Male fittings screw into a M5 Female equally well.  However, an M5 Male will not screw into a 10/32″ Female.

2. G 1/8″ and 1/8″ NPT Male fittings screw into a 1/8″ NPT Female equally well.  However a 1/8″ NPT Male will not screw into a G 1/8″ Female.

The 1/4″ and 3/8″ combinations do not work like this but 1/2″ and 3/4″ work reasonably well as they have the same threads per inch. In general BSPPT (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 sorts of things.  The above information is a layman’s explanation. If you have any comments, corrections or additions please e-mail me at fvernooy@anver.com.  Any help is appreciated. Thanks