Speaking of the fire hose products, people may not know the differences of hose threading between NH (NST), NPT, and NPSH (IPT), especially for those not familiar with couplings and threading. Ignorance about these differences results in mismatched parts, leading to waste of money, time, and energy, let along frustration.
To match up fire hose devices correctly is a bit confusing most of the time. Here in this article we’ll give you helpful tips about how to match them up with ease. For potential buyers, we also offer adequate information that you should know before you purchase the right products.
First thing first, you need to know what the hose coupling is. In fact, it is a connector normally made of brass, stainless steel, or aluminum, and located on the end of a hose that couples, or connects, with a hose, tap, or water source.
Three basic things to learn are the size of the proper thread attachment (3/4”-6”), thread standard, and gender. It’s much easier to tell the gender differences by appearance. The male coupling has outside threads while the female one has inside threads. Storz, however, is a “sexless” quarter-turn quick coupling.
To identify what type of thread you need means more than just looking at the couplings on the hose. What matters is the stamp with initials of the thread type, which can also be found on a water source fitting or adapter. You may contact the local fire department for professional assistance if you have any problems with the stamps or initials on a fire hydrant.
In the worst-case scenario, there might be no stamp available, and you need to carefully count the threads per inch. Not only that, the outside diameter of the male coupling is to be measured accurately, which can be a very tricky thing to do.
Well, let’s go back to the issue of the initials for a moment. Finding the right initials you need in order to identify the proper threading will seem like looking for a needle in the haystack because the number of threads are beyond your imagination. To make you breathe a little easier, you only need to know three major types of threads, i.e., NH/NST, NPT, and NPSH/IPT. This thread alphabet soup is unriddled as follows:
NH represents National Hose and NST means National Standard Thread, which are commonly used by fire departments to indicate “fire hose thread” on most of the fire hydrants and their accessories. Male NH/NST are only compatible with female ones and vise versa, but not other thread types unless proper adapters are used.
NPT, the abbreviation for National Pipe Tapered standards, is the US national technical standards for screw threads used on threaded pipes and pipe fittings. Male NPT matches not only female NPT but also NPTF, NPSM, and NPSH. Female NPT matches either male NPT or NPTF.
NPSH and IPT means the same standards, referring to National Pipe Straight Hose and Iron Pipe Thread, respectively. NPSH, a straight thread, is mostly used on low-pressure water suction and discharge hose couplings. Male NPSH is compatible with female NPSH and NPSM while female NPSH with male NPSH, NPT, NPTF, and NPSM. Understanding how to match the right fire hose threads and couplings might seem confusing, or even frustrating, but it is by no means a vain effort. With the basic knowledge and solid resources in your back pocket, you can minimize the risk of guesswork and mismatched couplings and hoses.