How it connects
Mates by screwing into an internal (female) thread; thread taper of 1:16 wedges flanks together as tightened. Requires thread sealant (PTFE tape or pipe dope) to fill spiral leak paths across crests and roots.
Male and female halves
Male external thread, mates with female internal thread (NPT/FPT/FIP).
Usually connects to
- Matching female NPT/FPT pipe fitting, including S&D cleanout adapters/hubs
- NPSM female straight thread only for the appropriate compatible assembly
Common sizes
- NPT nominal range 1/16–24 in; common residential/commercial sizes 1/8–2 in.
- Larger examples include 3, 4 and 6 in; nominal 6 in has about 6.625 in (168 mm) OD and 8 TPI.
Where it is used
residential plumbing; commercial plumbingHVACwater heaterscompressed air systemsgas piping; Gravity sewer pipingSewer and drain (S&D) systemsStormwater and landscape drainageSanitary cleanout access points
Variations
- NPTF (Dryseal USA Standard Taper Pipe Thread)
- NPSM (Straight Mechanical)
- NPTR (Railing)
- Raised square head cleanout plug
- Countersunk square/hex socket cleanout plug
How to recognise it
Recognizable by external tapered threads (slightly narrower at the opening) with 60-degree flank angle and flat crests and roots. Typically installed with PTFE tape or paste on the threads.
Often confused with
| Confused with | How to tell them apart |
|---|---|
| NPTF male thread | Identical taper and pitch, but NPTF has controlled crest and root truncation designed to crush metal-to-metal without thread sealant. |
| BSPT (R) male thread | BSPT has a 55-degree Whitworth thread angle and rounded crests/roots, whereas NPT has a 60-degree flank angle and flat crests/roots; pitch also differs on most sizes. |
| NPS straight pipe thread | NPS threads are parallel/straight along the full length, whereas NPT has a 3/4 inch per foot (1:16) taper. |
| Schedule 40 DWV cleanout plug thread | Both utilize standard ASME B1.20.1 NPT/MPT pipe thread dimensions, but S&D cleanouts mate with thin-wall Sewer & Drain ASTM D2729/D3034 adapters rather than heavy Schedule 40 (ASTM D2665) plumbing fittings. |
| S&D hub / spigot solvent-weld joint | The cleanout plug interface is a removable threaded male connection, whereas pipe hubs and spigots are smooth unthreaded cylindrical surfaces joined permanently with PVC primer and solvent cement. |
Also called
MIPMNPTNPT maleMale Iron PipeS&D MPTSewer & Drain cleanout plug threadS&D male pipe threadPVC cleanout plug thread
Good to know
Often labelled colloquially as MPT (Male Pipe Thread) or MIP (Male Iron Pipe) in retail plumbing and HVAC documentation.
Related connections
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