Pipe fittings · Adapter
3/8" NPT Female to 3/8" BSPT Male Adapter
3/8" NPT Female to 3/8" BSPT Male Adapter: one end takes a male 3/8" NPT (18 TPI) thread, the other screws into a female 3/8" BSPT · R (19 TPI) port. Drawing, 3D model, specs, where to buy, and a printable STL you can customize.
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What this fitting does
This adapter joins two different pipe thread systems. One end is a female 3/8" NPT (18 TPI) thread (NPT, the American standard). The other end is a male 3/8" BSPT · R (19 TPI) thread (BSPT, the British standard, stamped "R" under ISO 7-1). Use it when equipment from Europe, the UK, Australia or Asia (pumps, filters, valves, gauges) has to connect to American pipework, or the other way round.
Both threads are the same nominal size and both are tapered 1:16, so they look almost identical — but they do not seal together. NPT uses a 60° thread angle with 18 threads per inch; BSPT uses a 55° angle with 19 threads per inch. Forcing one into the other leaves leak paths, which is exactly why this adapter exists.
Specifications
| End 1 | End 2 | |
|---|---|---|
| Thread | 3/8" NPT (18 TPI) | 3/8" BSPT · R (19 TPI) |
| Gender | Female | Male |
| Standard | NPT | BSPT |
| Thread angle | 60° | 55° |
| Threads per inch | 18 | 19 |
| Major diameter | 17.145 mm | 16.662 mm |
| Taper | 1:16 | 1:16 |
| Thread length | 14 mm | 14 mm |
| Body | Hex 28 mm across flats | Neck 6 mm |
Also known as
People search for this part under many names. They all mean the same fitting:
- 3/8 FNPT x 3/8 MBSPT
- 3/8" NPT female x 3/8" BSPT male
- 3/8 inch NPT to 3/8 inch BSPT adapter
- NPT to BSPT adapter 3/8"
- 3/8 BSPT male to 3/8 NPT female
- R 3/8 to 3/8 NPT
- 3/8 FIP x 3/8 BSPT MIP
- 3/8-18 NPT to 3/8-19 BSPT
- adapter NPT BSPT 3/8
- American to British pipe thread adapter 3/8"
How to install it
Wrap 3–4 turns of PTFE tape (or use thread sealant) on each male thread, clockwise as you look at the end. Tighten hand-tight, then 1–2 more turns with a wrench on the hex. Both ends seal on the threads, so no washer is needed. Check for drips after the water is turned on.
Where to buy one
Ready-made versions in brass or stainless steel are sold by these stores (links open a search):
Need a different length or size?
Open this fitting in the designer, change any dimension, test-fit a print, then order the final part from a professional print service.
Learn more: NPT vs BSP explained · pipe fitting types