Quick question: Do you know the differences between NH (NST), NPT, and NPSH (IPT) when it comes to fire hose threading? If you aren’t familiar with different types of fire hose fittings and couplings, these questions can be pretty confusing.
Not understanding these differences can lead to mismatched parts, which leads to loss of money and time, not to mention plenty of frustration.
Many factors go into matching different fire hose components together. We’re here to clear up some of the mystery and give you some great resources to keep handy for when you do need to purchase and match the right products.
Couplings and Threading Basics
First, what are hose couplings? A hose coupling is a fire hose fitting that is located on the end of a hose. It couples, or connects, with a hose, tap, or water source, and is typically made of brass, stainless steel, or aluminum.
The key characteristics to understand with regard to proper thread attachment are size (3/4” to 6”), thread standard, and gender. Male coupling has threads on the outside, while female coupling has threads on the inside. When you have 2 fire hose fittings, you’ll need one to be male and one to be female.
Some couplings are “sexless.” Storz, for example, is a quarter-turn quick connection.
The easiest way to identify what type of thread you need is by looking at the couplings on the fire hose you want to replace. There should be a stamp with the initials of the thread type. A water source fitting/adapter may also have the stamp. If you need to know what to use on a fire hydrant, call the local fire department.
If there’s no stamp available, you can carefully count the threads per inch and measure the outside diameter of the male coupling; however, this can be a very tricky procedure.
Fire Hose Thread
What initials should you use to identify the proper threading? There are many threads out there, but three are used primarily: NH or NST, NPT, and NPSH or IPT.
NH stands for National Hose and NST stands for National Standard Thread. This is often referred to as “fire hose thread” because fire departments use it the most. It’s popular on many fire hydrants and accessories. Garden hose thread (GHT) is also referred to as NH.
Compatibility: Male NH/NST to Female NH/NST; Female NH/NST to Male NH/NST. Because these are not compatible with other thread types, fire hose thread adapters are used to connect the different types of couplings.
NPT stands for National Pipe Tapered and is mostly used in plumbing and industrial. It’s recommended to use plumber’s tape or thread-sealing paste. NPT is compatible with NPSM threads if you choose male NPT to female NPSM (see below), whereas NPT vs GHT is not compatible. NPT is sometimes also called pipe thread.
Compatibility: Male NPT to Female NPT, NPTF, NPSM, NPSH; or Female NPT to Male NPT or NPTF.
NPSH stands for National Pipe Straight Hose. IPT stands for Iron Pipe Thread. NPSH is a straight thread and is popular on low-pressure water suction and discharge hose couplings.
Compatibility: Male NPSH to Female NPSH, NPSM or Female NPSH or Male NPSH, NPT, NPTF and NPSM.
Knowing what goes into fire hose threading and coupling might seem confusing at first, but knowing the basics and having some solid resources at your disposal takes the guesswork out of the process.
Need a custom threading or coupling solution? Rawhide Fire Hose can help you find the hose you need.