Comparison of NPT and NPS pipe threads
NPT threads are tapered and NPS threads are cut straight. NPT threads are cut deeper (smaller diameter) into the end of the pipe and taper to the outside diameter of the pipe. NPS threads are cut the same depth or straight for the whole thread. They both are cut at 11.5 threads per inch and use a 60 degree thread form. Our products use NPT but in some cases will work with NPS threads.
Also called National Pipe Taper (NPT) and National Pipe Straight (NPS), or tapered and straight pipe thread. Same size, same 60 degree form.
The main difference
The main difference in NPT (National Pipe Taper) and NPS (National Pipe Straight) threads is NPT threads are tapered and NPS threads are cut straight. NPT threads are cut deeper (smaller diameter) into the end of the pipe and taper to the outside diameter of the pipe. NPS threads are cut the same depth or straight for the whole thread. They both are cut at 11.5 threads per inch and use a 60 degree thread form. Our products all use NPT threads. We have tested our pipe and adjustable masts to thread securely with some manufacturers' NPS female threads.
What we have tested
We tested our pipes and adjustable masts to thread securely into some manufacturers' NPS female threads. Below you can see our 6 inch pipe threads solidly into the Axis T94A01D pendant kit. Our tapered threads usually thread in about 3 to 4 full turns (about 1/4 to 1/3 of the way), since the NPS threads are not tapered, our pipe threads in further, about 2/3 of the way down the thread before the diameter of the pipe meets up with the internal diameter of the female thread.
Our recommendation is you can use our pipes or adjustable pipes/masts to thread into a female NPS thread, but we would not recommend using NPS threaded pipes with our female NPT threads.
Common questions
Are NPT and NPS interchangeable?
Sometimes. They both use 60 degree angle thread form and 11.5 threads per inch, so an NPT male and an NPS female of the same size thread together. If you are not sure about a specific part, call us and we can check.
Why does an NPT to NPT connection stop after only 3 to 4 turns?
Because the thread is tapered. It is like driving a wedge in, there is only so far it can go. The NPT threads are commonly used for pipe connections that need to seal. For a mechanical use like hanging a TV, it is not necessary, but it is what the industry has chosen to use.
How do I tell if a product uses NPT or NPS?
Look for the manufacturers' specifications. Many products will have a spec sheet or dimensioned drawing that calls out what type thread is used. Most of the time you can look at the male threads and tell if they taper off towards the end of the thread. If the tips of the threads run in a line parallel to the OD or ID of the tube they are in, those would be NPS threads. If they taper, it is an NPT thread. Refer to the diagram above for an example. If you are unsure call or contact us for assistance.
We have another blog post about the NPT thread.
Keep building your setup
Not sure which thread you have?
Send us a measurement and we will tell you.
References: National Pipe Thread (NPT and NPS), ASME B1.20.1 pipe threads (general purpose).