How it connects
Parallel threads only hold the parts together; the seal comes from a rubber/fibre flat washer (plumbing) squeezed between the male end face and the female nut, so hand-tight plus a little torque seals without tape.
Male and female halves
This is the male (external thread) half. The female half is usually a captive swivel nut containing the gasket (hose end); in hydraulics the female NPSM swivel instead seals on a 30° cone seat.
Usually connects to
- Matching female NPSM washer-sealed shower nut or hydraulic 30°/37° seat variant
- Female NPT fitting is a loose fit and not recommended without appropriate sealant
- Matching NPSL/NPSM conduit locknut or NPSC/NPSM/NPT hub
- Matching insulated throat bushing
- Electrical enclosure knockout through the mounting hardware
Common sizes
- NPSM trade ranges commonly span 1/8–6 in, with descriptions extending to 12 in; many electrical fittings use 3/8–4 in, especially 1/2, 3/4, 1, 1-1/4, 1-1/2 and 2 in.
- Shower connections commonly 1/2-14, about 20.8 mm OD; hydraulic swivels commonly 1/4–1-1/4 in.
Where it is used
Residential showers/handshowers/hosesHydraulic swivels and pressure-washer/fluid fittingsRigid/IMC/liquidtight conduit installationsJunction boxes/panel enclosuresIndustrial mechanical/plumbing equipment
Variations
- Standard NPSM straight male hub, straight/45°/90°
- Washer-sealed flat face for plumbing
- 30° hydraulic cone seat
- Related NPSL locknut or NPSC coupling thread
- Zinc die-cast, malleable iron or steel
How to recognise it
Short parallel external thread (about 14 threads per inch on 1/2 in.), usually with a smooth flat end face or shoulder for the washer and no thread sealant; mating part is a knurled or hex swivel nut with a rubber washer inside. Typical on US shower arms and the hose ends of hand showers.
Often confused with
| Confused with | How to tell them apart |
|---|---|
| NPT pipe thread | NPT diameter tapers toward the end and seals on the threads with tape/dope; NPSM is constant diameter and relies on a washer. Same 14 TPI at 1/2 in., so they partly thread together. NPT has a 1:16 taper and seals by thread interference; NPSM is parallel (straight diameter along the entire length) and does not jam to seal. |
| G1/2 BSPP (ISO 228-1) | BSPP 1/2 has 14 TPI too but 55° thread angle and ~20.96 mm OD vs 60° and ~20.8 mm for NPSM; European/UK showers use G1/2. Usually needs the product origin or a thread gauge to tell. |
| Garden hose thread (GHT/NH) | GHT is 3/4-11.5, larger and coarser than 1/2-14 NPSM. |
| NPSL Thread | NPSL has looser tolerances specifically standardized for locknut fastening on conduit; NPSM has standard free-fitting mechanical pipe tolerances. |
| NPSC Thread | NPSC applies to internal (female) straight pipe threads in rigid conduit couplings, whereas NPSM is a mechanical joint straight thread. |
Also called
1/2-14 NPSM1/2 in. IPS straight thread (shower)straight pipe thread male; Mechanical straight pipe thread; Straight conduit hub thread; straight conduit male thread; Conduit male hub with locknutshower hose threadNPSM male thread; NPSL male threadParallel conduit entry threadNPS male enclosure threadLiquidtight male connector hub
Good to know
A US hand-shower connection is commonly 1/2-14 NPSM; G1/2 BSPP is an alternative on non-US products. Hydraulic NPSM cone-seat swivels are a different sealing arrangement from plumbing washer seals.
Related connections
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