Couplings, nozzles, valves, adapters are just a few essential fittings that use screw threads to connect plumbing pipes or hoses used to run liquid or air. The U.S. and Canada use guides set by ANSI-ASME to unify fittings, such as the garden hose thread (GHT) and national pipe taper (NPT).
Even if they seem to be alike, the truth is, one cannot fit with the other. The GHT has a parallel thread, while the NPT has tapered threads. Essentially, you will use a GHT to connect garden hose fittings while you’ll use NPT threads for plumbing and pipe fittings.
What are GHT and NPT?
Garden hose threads (GHT) are screw thread standards set by ANSI-ASME B1.20.7 for couplings, fittings, nozzles, and valves for hoses. On the other hand, National pipe taper threads (NPT) are screw thread standards set by ANSI-ASME B1.20.1 for threaded pipes and fittings.
GHT has parallel threads, which require gaskets or O-rings to seal when connected. NPT has tapered threads. They are supposed to seal shut, but they tend to loosen. So they need Polytetrafluoroethylene (PTFE) tape to be leak-free.
For this reason, GHT and NPT threads are not compatible with each other.
GHT vs. NPT: Standard
The American standard uses the guidelines set by ANSI-ASME B1.20.7 for joining hoses and fittings or officially called National hose or NH. The pitch required for GHT must have 11.5 TPI or threads per inch. External diameter must measure 1 1/16”. Use NHR for threads thin-walled fittings and NH for thick-walled couplings. Garden hose sizes come in 1/2”, 5/8”, and 3/4“. The term for male hose thread is MHT and the term for female hose thread is FHT.
The NPT is an American standard set in ANSI-ASME B1.20.1 for joining pipes and fittings. The center axis and taper joint would require an angle of 1° 47′ 24” (1.7899°).
Since NPTs are tapered threads, the TPI varies as the size increases. An NPT thread of 3/4” would have an external diameter or OD of 1.050” and a pitch of 14 TPI. Although not authorized designation, you can refer to male pipe threads as MPT and female pipe threads as FPT.
GHT vs. NPT: Hose diameter
In the US, 3/4” GHT fitting would be compatible with garden hoses having 1/2”, 5/8”, or 3/4” internal diameter. That’s not the case for pipe fittings. Pipe fittings would have gradually compressing internal diameter as it gets tapered. For this reason, NPT adapters should be free of burr. They require lubricants or PTFE tape for leak-free pipe and coupler joining.
A 3/4” pipe thread would have a 1.050” OD. With a 1/2” ID pipe thread of 3/4”, the fitting will have an OD of 0.840”. A 5/8” NPT thread of 3/8” ID will have 0.675”. If you notice, the tapering OD fitting will compress the ID NPT fitting gradually.
GHT vs. NPT: Where and how to use them?
Garden hose thread applications include joining hoses and couplers so that water or liquid can run through the hose. These couplers could either be threads for spigots, faucet, Silcock, bibcock, or hose bib.
National pipe taper thread applications include joining pipes and fittings to transport liquid, steam, air, or hydraulic liquid. Usually made of brass or steel, these fittings can be elbows, valves, reducers, couplings, caps, or tees.
Here are the basics of NPT fittings and how they work.
GHT vs. NPT: Prices
Depending on the material, garden hose fittings may go as low as a couple up to five hundred bucks. The cheapest goes for plastic-made hose fittings. Brass-made fittings are high-end but more durable.
For pipe fittings, stainless steel threads can be as low as one dollar. Chrome-plated brass fittings can get as high as six hundred dollars and more. These plating requirements are mostly due to added protection and corrosion resistance, depending on the air or liquid substance that will run on the pipe.
GHT vs. NPT: Tools needed
Ideally, you may need wrenches, reducers, and hose clamps to join garden hoses and fittings of different sizes.
Screwing pipe and fittings together may need the help of clamping tools or vises and plumbing wrenches or pliers.
GHT vs. NPT: Quick Comparison
Item: (based on 3/4” thread size)
Garden hose threads (GHT)
National pipe taper (NPT)
1.062” or 1 1/16”
Applications and uses
For transporting water for landscaping, lawn care, and gardening
For transporting air. Liquid, gases, hydraulic acid, or steam
Faucet, spigots, tap, bibcock, Silcock, and hose bib
Elbows, tees, valves, reducers, caps, couplings
$2 to $500 plus
$1 to $600 plus
O-rings or rubber washers
Plastic, stainless steel, brass, copper
Stainless steel, carbon steel, brass, copper
Garden hose threads and national pipe tapers are completely different screw threads. GHT has parallel threads, while NPT has tapered threads. GHTs are for gardening and landscaping use while NPTs are for plumbing systems. Both threads do not fit each other, so you cannot use them together in one joint.
Now that you know the differences between GHT and NPT, it’s time to check your fittings and see which ones are fit for your project.