NPS, NPT, NP what? In this article, we're going to explain the differences and similarities between NPS and NPT fittings.
First of all, what do they stand for? Both are acronyms for a standard of thread used in the plumbing industry. NPS stands for National Pipe Straight, and NPT stands for National Pipe Tapered. Okay, so with that out of the way, why is it important to know the difference?
Fundamentally, the difference is in the application. Straight-threaded fittings have threads that are perfectly parallel. The diameter of the threads does not vary from one end of the threaded length to the other end. This allows a fastener or nut to thread up and down freely along the entire length of that thread. Picture a nut on a bolt. You can run it up and down the entire length with no restriction. A tapered threaded fitting has threads that get gradually larger from the open end of the thread to the end of the threaded system. This allows for a secure connection when threaded fittings are mated together. The tapers of the fitting, the female side and the male side match each other, and it actually creates a binding that makes for a water- or even airtight connection.
Great, so when is each one used? NPS is frequently used for ballast system solutions and applications where the part is mating into a surface of varying thickness. For example, a thru-hull fitting that passes through the hull of the boat and the nut that retains it on the inside will need to be flexible enough to accommodate varying thicknesses of holes. In that scenario, a straight-threaded connection makes more sense because the nut can thread up and down freely and provide a clamping force wherever it needs to based on the thickness of the hole.
NPT threaded connections, on the other hand, are frequently used where plumbing connections meet each other. If you're threading a ball valve onto the end of a through-hole fitting, for example, you're going to want a tapered connection there, so that as the ball valve tightens on, you get that secure watertight connection.
Are NPT and NPS Compatible
In most cases, you don't need to be aware of this. We've taken care of all the hard work and ensured that all the fittings are compatible. Certainly, if you're using one of our pre-designed solutions, it's all taken care of for you. If you're trying to piece together your own solution though, it's something to be aware of and a product expert can help you ensure that you have the correct fittings based on the connections that you're making up. Contact us if you have any additional questions.