# BSP (G) male thread envelopes 1/8 to 1 in (ISO 228-1)

> What is the outside diameter of a G1/4 BSP thread?

- Category: Hardware › Stirling & thermoacoustic
- Kind: Hardware
- Basis: ISO 228-1 (G, parallel) and ISO 7-1 (R / Rc, taper) BSP major diameters and TPI
- Page: https://xemstudio.com/objects/bsp-thread-envelopes/ · JSON: https://xemstudio.com/api/geometry?object=bsp-thread-envelopes · Plain text: https://xemstudio.com/objects/bsp-thread-envelopes/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); linked files under their publishers' licenses

**Exact dimensions.** True size, with no printing tolerance added.

## Notes

- Each file is a plain cylinder at the BSPP (G) major OD, 14 mm long, with a 0.8 mm chamfer on the end; the thread form is not modelled.
- Major OD: G1/8 9.73, G1/4 13.16, G3/8 16.66, G1/2 20.96, G3/4 26.44, G1 33.25 mm; 28, 19, 19, 14, 14 and 11 TPI.
- BSP is a 55° thread; parallel G seals on a washer or O-ring, taper R on the thread.
- BSP and NPT do not interchange: 1/2 NPT is 14 TPI 60° and 21.34 OD, G1/2 is 14 TPI 55° and 20.96 OD.

## Sizes

| size | od_mm | tpi | file_length_mm |
|---|---|---|---|
| G1/8 | 9.73 | 28 | 14 |
| G1/4 | 13.16 | 19 | 14 |
| G3/8 | 16.66 | 19 | 14 |
| G1/2 | 20.96 | 14 | 14 |
| G3/4 | 26.44 | 14 | 14 |
| G1 | 33.25 | 11 | 14 |

## Where the files are

- Wikipedia: [National pipe thread](https://en.wikipedia.org/wiki/National_pipe_thread) — web — CC BY-SA 4.0 (text)
- Wikipedia: [British Standard Pipe](https://en.wikipedia.org/wiki/British_Standard_Pipe) — web — CC BY-SA 4.0 (text)
- Long Earth Society: [Engine builds that use these parts (videos and write-ups)](https://longearthsociety.com/engineering/) — web, video — LES site

## Free STEP/STL (6 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/bsp-thread-envelopes/index.json

- bsp-1-8-male: [STEP](https://xemstudio.com/files/hardware/npt-bsp-thread-envelopes/bsp-1-8-male.step) · [STL](https://xemstudio.com/files/hardware/npt-bsp-thread-envelopes/bsp-1-8-male.stl) — G1/8 BSPP male, major OD 9.73 mm, 28 TPI, 14 mm; plain cylinder at OD
- bsp-1-4-male: [STEP](https://xemstudio.com/files/hardware/npt-bsp-thread-envelopes/bsp-1-4-male.step) · [STL](https://xemstudio.com/files/hardware/npt-bsp-thread-envelopes/bsp-1-4-male.stl) — G1/4 BSPP male, major OD 13.16 mm, 19 TPI, 14 mm; plain cylinder at OD
- bsp-3-8-male: [STEP](https://xemstudio.com/files/hardware/npt-bsp-thread-envelopes/bsp-3-8-male.step) · [STL](https://xemstudio.com/files/hardware/npt-bsp-thread-envelopes/bsp-3-8-male.stl) — G3/8 BSPP male, major OD 16.66 mm, 19 TPI, 14 mm; plain cylinder at OD
- bsp-1-2-male: [STEP](https://xemstudio.com/files/hardware/npt-bsp-thread-envelopes/bsp-1-2-male.step) · [STL](https://xemstudio.com/files/hardware/npt-bsp-thread-envelopes/bsp-1-2-male.stl) — G1/2 BSPP male, major OD 20.96 mm, 14 TPI, 14 mm; plain cylinder at OD
- bsp-3-4-male: [STEP](https://xemstudio.com/files/hardware/npt-bsp-thread-envelopes/bsp-3-4-male.step) · [STL](https://xemstudio.com/files/hardware/npt-bsp-thread-envelopes/bsp-3-4-male.stl) — G3/4 BSPP male, major OD 26.44 mm, 14 TPI, 14 mm; plain cylinder at OD
- bsp-1-male: [STEP](https://xemstudio.com/files/hardware/npt-bsp-thread-envelopes/bsp-1-male.step) · [STL](https://xemstudio.com/files/hardware/npt-bsp-thread-envelopes/bsp-1-male.stl) — G1 BSPP male, major OD 33.25 mm, 11 TPI, 14 mm; plain cylinder at OD

## How it fits

### Connects to
- [Push-fit fitting envelopes: 4 / 6 / 8 mm tube, G1/8 and G1/4 thread stubs](https://xemstudio.com/objects/push-fit-fittings/): G1/8 and G1/4 thread stubs on the push-fits

### Alternatives
- [NPT male thread envelopes 1/8 to 1 in (ASME B1.20.1)](https://xemstudio.com/objects/npt-thread-envelopes/): NPT is 60° and taper; not interchangeable

### Also needed
- [O-rings, common metric sizes (ISO 3601)](https://xemstudio.com/objects/o-rings-metric/): parallel G threads seal on an O-ring or washer

## Questions

**What is the OD of G1/4?**

13.16 mm, 19 TPI, 55° thread.

**Are NPT and BSP interchangeable?**

No: NPT is 60° and BSP 55°, the ODs differ (1/2 NPT 21.34 vs G1/2 20.96 mm) and 1/8, 1/4 and 3/8 have different TPI.

## Fits with

- [NPT male thread envelopes 1/8 to 1 in (ASME B1.20.1)](https://xemstudio.com/objects/npt-thread-envelopes/)
- [Push-fit fitting envelopes: 4 / 6 / 8 mm tube, G1/8 and G1/4 thread stubs](https://xemstudio.com/objects/push-fit-fittings/)
- [O-rings, common metric sizes (ISO 3601)](https://xemstudio.com/objects/o-rings-metric/)