Quickly identify pneumatic thread size and type from AutomationDirect

In this video, we’ll see how to easily identify the thread size and type used in your pneumatic systems. Threaded pneumatic fittings are threaded with one of 3 standard pipe threads. These are National Pipe Taper, British Standard Pipe Taper or British Standard Pipe Parallel. Here’s an example of NPT threads on a pipe. Notice the OD of the pipe is close to 1/2” but this is ¼” pipe. This is because the pipe is sized by inside diameter but the threads are obviously on the outside. The easiest way to determine a pipe thread size is to measure the thread outside diameter and subtract ¼”. The harder part is figuring out which of the 3 standards the threads are. Parallel, or straight threads, maintain a consistent diameter like a bolt. Parallel threads require an O-ring or other gasket to seal. Tapered threads have an increasing or decreasing diameter depending on how you look at them. Tapered threads seal in the threads with the aid of a sealant like thread tape or paste. If you have inch or SAE sized tubing you likely have NPT treads. If your tubing is metric you likely have a British Standard Pipe thread. There are some exceptions to this we’ll cover in a minute. Also if you know where the machinery was manufactured it can be a clue. In the US, NPT is most commonly used. Chinese and Japanese equipment often use BSPT and Europeans commonly use BSPP. Since there is only one standard that has parallel threads, if your part has straight threads you can safely assume it is BSPP or G thread. If you have tapered threads you need accurate measurements since BSPT and NPT have close or the same thread pitch. You may assume since the thread pitch and diameters are nearly the same with BSPT and NPT you can interchange them but this will not work. The threads on these 2 standards are cut at a different angle and shaped slightly differently. A thread pitch gauge can show this. Now for some interesting notes. There are some fittings that convert between metric and US standards such as 10mm tubing to 3/8 inch NPT. These are hard to find and generally quite expensive so they are seldom used. However, 2 tubing sizes are interchangeable between metric and inch. These are 4mm which is close enough to 5/32” to work as either and 8mm which interchanges with 5/16”. There are 2 very small fittings sometimes used that do not follow these standards. These are 10-32 and M5 x 0.8. These are both parallel threads and use an o-ring to seal. So if you find a fitting that is smaller than listed in the standards tables, see if they match these. AutomationDirect is providing the products and support you need to make us your common sense way to buy industrial controls and pneumatics. Please see other videos in this pneumatics series to understand valves, cylinders, and other pneumatic components. We have a vast library of other videos. Please click here to view all product videos. Click here to subscribe to our YouTube channel for upcoming products and solutions.