Connection standard
NPT tapered pipe thread on pressure washer guns and fittings
How to recognize NPT: a 60-degree tapered thread with 18 TPI at 1/4 and 3/8 in that seals with sealant, the FPT and MPT ports on pro guns, and its BSPT look-alike.
Also listed as NPT, NPTF, FPT, MPT, FNPT, MNPT
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Short answer
NPT is the US tapered pipe thread (ASME B1.20.1), with a 60-degree thread angle and 18 threads per inch at 1/4 and 3/8 in. It seals on the thread with a sealant, unlike M22, which seals on an O-ring. Professional guns use it: Suttner lists most of its guns with a 3/8 in FPT inlet and 1/4 in FPT outlet, and MTM's SGS28 has the same ports. Dixon says female NPT is not available on hose swivel nuts.
Key facts
- How to recognize it
- On a disconnected, depressurized part only: measure the diameter at the start and end of the thread with calipers (a tapered thread gets smaller, Dixon says), then find the pitch: 1/4 and 3/8 in NPT have 18 threads per inch[1][2]Swagelok's identification steps: tapered or straight, diameter, pitch, standard, then end connection.
- Thread
- Tapered pipe thread, 60-degree thread angle, taper 1 degree 47 minutes; 18 TPI at 1/4 and 3/8 in. ASME B1.20.1 is the US standard. In '1/2-14 NPT', 1/2 in is the nominal pipe inside diameter and 14 is threads per inch[2][3][1]
- How it seals
- On the threads: Swagelok says tapered pipe threads seal on the threads and always need a sealant[2]
- Male and female ends
- FPT is female pipe thread and MPT male. Suttner lists most of its guns with a 3/8 in FPT inlet and a 1/4 in FPT outlet; MTM's SGS28 has a 3/8 in FPT inlet with a live swivel and a 1/4 in FPT outlet. Dixon says female NPT is not available on hose swivel nuts[4][5][1]
- Where makers use it
- Professional guns and fittings: Suttner guns, MTM SGS28, MTM PRIMA couplers and plugs (1/4 in MPT and FPT), Reelcraft's PW81000 reel (1/2 in NPT(F) inlet, 3/8 in NPT(F) outlet), Obsessed Garage's 3/8 in hose (NPT fittings, one swivel end)[4][5][6][7][8]
- Adapters makers sell
- MTM PRIMA by Veloci couplers and plugs pair a 1/4 or 3/8 in quick-connect with an MPT or FPT thread. A retailer lists the Mosmatic DGV swivel 32.557 with 1/4 in NPTF on both ends[6][9]The Mosmatic figures are a retailer's listing for variant 32.557 only.
- Ratings on parts
- Suttner ST-2305: 5,000 PSI, 12 GPM; ST-1100: 3,050 PSI, 7 GPM; ST-2000: 5,000 PSI, 10.4 GPM. MTM SGS28: 4,000 PSI, 12 GPM, 320°F. Mosmatic DGV 32.557: 4,000 PSI and 250°F, as a retailer lists[4][5][9]Suttner's range page lists no temperatures.
- Common mix-ups
- BSPT is also tapered, but 55 degrees and 19 TPI at 1/4 and 3/8 in; Swagelok says 1/2 and 3/4 in sizes are hard to tell apart without an optical comparator. M22 is a straight metric thread that seals on an O-ring; MTM's SGS28 NPT gun is not a direct fit for M22 hoses[2][5]
- Not confirmed
- Not confirmedMeasurement tolerances (Dixon says measured values may differ slightly from its charts, without a figure); Mosmatic's own DGV data; temperature ratings for Suttner guns.
Watch out for
- Do not carry NPT sealant habits over to M22 or quick-connect O-ring joints; Swagelok says straight threads need no sealant.
- Mosmatic DGV figures are a retailer's listing for variant 32.557 only; Mosmatic's own pages could not be read.
- NPT's nominal size refers to the pipe's inside diameter, while a metric M size is the thread's outer diameter (Dixon), so do not size a pipe thread with a ruler alone.
- Swagelok warns that even experienced workers sometimes have difficulty identifying threads.
What fits
Product details below are the seller's own description unless a source is shown. Pick the variant named for each item.
Spray gun, FNPT ports
SIMPSON 80178 professional pressure washer spray gun, 5,075 PSI, hot and cold water, with M22 and QC adaptersChoose the 80178 gun with M22 and QC adapters.
SIMPSON lists a 3/8 in FNPT inlet and a 1/4 in FNPT outlet, with M22 and quick-connect adapters included.
Questions
How do I tell NPT from BSPT?
Swagelok gives NPT a 60-degree thread angle and 18 TPI at 1/4 and 3/8 in, and BSPT a 55-degree angle and 19 TPI at those sizes. Both are tapered, and 1/2 and 3/4 in sizes can be hard to tell apart without an optical comparator. See NPT, BSP and M22.[2]
Does an NPT thread need sealant?
Yes. Swagelok says tapered pipe threads seal on the threads and always need a sealant. Straight threads, such as M22, seal on a gasket or O-ring instead.[2]
Can I screw an M22 hose into an NPT gun?
Not directly. MTM's SGS28, for example, has 3/8 in FPT inlet and 1/4 in FPT outlet pipe-thread ports, not M22, so a consumer M22 hose needs suitable fittings.[5]