# BSP taper pipe threads R and Rp (ISO 7-1), 1/16 to 6: TPI, pitch, gauge-plane diameter, gauge length + 8 male taper STEP/STL files

> What are the dimensions of an R 1-1/4, R 2 or R 3 BSPT taper pipe thread: TPI, pitch, major diameter at the gauge plane, pitch diameter and gauge length?

- Category: Tri-clamp & pipe › Pipe, tube & threads
- Kind: Standard part
- Basis: ISO 7-1 sample Table 1 (d, d2, d1, pitch) with gauge length from Engineering ToolBox and Wikipedia; EN 10255 tube sizes for the example stubs; McMaster-Carr pipe fittings linked
- Page: https://xemstudio.com/objects/bsp-taper-pipe-threads-r-rp-iso-7-1/ · JSON: https://xemstudio.com/api/geometry?object=bsp-taper-pipe-threads-r-rp-iso-7-1 · Plain text: https://xemstudio.com/objects/bsp-taper-pipe-threads-r-rp-iso-7-1/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); files CC BY 4.0 or their publisher's license
- Use in every chat: add https://xemstudio.com/mcp as a connector (https://xemstudio.com/use-with-ai/)

**Exact dimensions.** Every file is drawn at true size with no tolerance added. The holes and pins that meet another part are listed below under Mating features, with the fit each joint needs; open those by your process's clearance before making the part.

## Notes

- R is the external taper pipe thread (taper 1:16 on diameter), Rp the internal PARALLEL thread and Rc the internal taper thread (ISO 7-1 designations). The diameters above are at the gauge plane; the thread gets 1 mm smaller in diameter for every 16 mm toward the end. The gauge length a is the distance from the gauge plane to the small end of the external thread.
- Numbers: ISO 7-1 sample Table 1 (iTeh) for the pitch, d, d2 and d1 of all 15 sizes (the generator re-checks P = 25.4 / TPI, d2 = d - 0.640327 P and d1 = d - 1.280654 P on every row); gauge length a from Engineering ToolBox's ISO 7-1 table and the Wikipedia British Standard Pipe table, which agree on 1/8, 1/2 and 1. R 4 and R 5 gauge lengths (25.4, 28.6) come from Engineering ToolBox only and R 6 (28.6) from Wikipedia only: the iTeh scan's gauge-length column was not legible, so there is no second source for those three. The tolerance on gauge length, the useful thread length and the fitting allowance were not readable in the sample and are left out.
- Files: 8 male taper envelopes for R 1-1/4 to R 6. Each is a cone from the free end to the gauge plane (major Ø d at the gauge plane, Ø d - a/16 at the free end) joined to an EXAMPLE EN 10255 medium tube stub (30 mm long, our example length, OD and wall below). The stub OD is larger than d on every size, as in a real threaded tube. Sizes up to R 1 (and BSP 1/8 to 1 as plain male ends) are on the 'Pipe thread envelopes' page.
- EN 10255 medium tube used for the stub (OD x wall, mm): 1-1/4 = 42.4 x 3.25, 1-1/2 = 48.3 x 3.25, 2 = 60.3 x 3.65, 2-1/2 = 76.1 x 3.65, 3 = 88.9 x 4.05, 4 = 114.3 x 4.5, 5 = 139.7 x 4.85, 6 = 165.1 x 4.85. BS 1387 tables (Engineering ToolBox) give a slightly different OD for the same nominal bores (medium / heavy OD 42.9, 48.8, 60.8, 76.6, 89.5, 114.9, 140.6, 165.1) and walls (3.2, 3.2, 3.6, 3.6, 4.0, 4.5, 5.0, 5.0): the two standards differ, so the stub is an example, not a fixed size.
- Left out: Rc internal taper details, the Rp internal tolerances, NPT (ASME B1.20.1 has its own page), JIS PT, and BSPT in tapped-hole drill sizes.

## Mating features (exact size; open press / slide / run / socket by your process clearance, leave designed and clamp as drawn)

| feature | exact | mates with | fit | files |
|---|---|---|---|---|
| R male taper thread (gauge-plane Ø d) | R 1-1/4 to R 6: Ø41.910 to Ø163.830 at the gauge plane | the internal Rp (parallel) or Rc (taper) thread of the same size, 11 TPI for R 1 to R 6 (ISO 7-1 designations); the male cone is the file | designed | R-* |
| pitch Ø d2 | e.g. R 2: Ø58.135 | the same d2 at the gauge plane of the internal thread (Rp / Rc) | designed | R-* |
| example tube stub | EN 10255 medium tube OD 42.4 to 165.1 | plain tube of that OD (the stub is an example, see notes) | designed | R-* |

## Sizes

| size | TPI | pitch P, mm | major Ø d at gauge plane, mm | pitch Ø d2, mm | minor Ø d1, mm | gauge length a, mm | free-end major Ø (d - a/16), mm | source |
|---|---|---|---|---|---|---|---|---|
| R / Rp 1/16 | 28 | 0.907 | 7.723 | 7.142 | 6.561 | 4 | 7.473 | ISO 7-1 sample + ETB |
| R / Rp 1/8 | 28 | 0.907 | 9.728 | 9.147 | 8.566 | 4 | 9.478 | ISO 7-1 sample + ETB/Wikipedia |
| R / Rp 1/4 | 19 | 1.337 | 13.157 | 12.301 | 11.445 | 6 | 12.782 | ISO 7-1 sample + ETB/Wikipedia |
| R / Rp 3/8 | 19 | 1.337 | 16.662 | 15.806 | 14.95 | 6.4 | 16.262 | ISO 7-1 sample + ETB |
| R / Rp 1/2 | 14 | 1.814 | 20.955 | 19.793 | 18.631 | 8.2 | 20.442 | ISO 7-1 sample + ETB/Wikipedia |
| R / Rp 3/4 | 14 | 1.814 | 26.441 | 25.279 | 24.117 | 9.5 | 25.847 | ISO 7-1 sample + ETB/Wikipedia |
| R / Rp 1 | 11 | 2.309 | 33.249 | 31.77 | 30.291 | 10.4 | 32.599 | ISO 7-1 sample + ETB/Wikipedia |
| R / Rp 1-1/4 | 11 | 2.309 | 41.91 | 40.431 | 38.952 | 12.7 | 41.116 | ISO 7-1 sample + ETB |
| R / Rp 1-1/2 | 11 | 2.309 | 47.803 | 46.324 | 44.845 | 12.7 | 47.009 | ISO 7-1 sample + ETB |
| R / Rp 2 | 11 | 2.309 | 59.614 | 58.135 | 56.656 | 15.9 | 58.620 | ISO 7-1 sample + ETB/Wikipedia |
| R / Rp 2-1/2 | 11 | 2.309 | 75.184 | 73.705 | 72.226 | 17.5 | 74.090 | ISO 7-1 sample + ETB |
| R / Rp 3 | 11 | 2.309 | 87.884 | 86.405 | 84.926 | 20.6 | 86.597 | ISO 7-1 sample + ETB/Wikipedia |
| R / Rp 4 | 11 | 2.309 | 113.03 | 111.551 | 110.072 | 25.4 | 111.442 | ISO 7-1 sample; a from ETB only |
| R / Rp 5 | 11 | 2.309 | 138.43 | 136.951 | 135.472 | 28.6 | 136.643 | ISO 7-1 sample; a from ETB only |
| R / Rp 6 | 11 | 2.309 | 163.83 | 162.351 | 160.872 | 28.6 | 162.043 | ISO 7-1 sample; a from Wikipedia only |

## Where the files are

- iTeh Standards: [ISO 7-1:1982 sample: Table 1 basic dimensions of pipe threads (pitch, d, d2, d1) 1/16 to 6](https://cdn.standards.iteh.ai/samples/3583/8bb5ad0f36684c6cbebd554338fcde0d/ISO-7-1-1982.pdf) — web — Publisher's page; dimensions are facts
- Engineering ToolBox: [ISO 7-1 and ISO 228 pipe threads: TPI, pitch, diameters and gauge length (a)](https://engineeringtoolbox.com/iso-threads-d_752.html) — web — Publisher's page; dimensions are facts
- Wikipedia: [British Standard Pipe: G / R size table (major and minor diameters, gauge length)](https://en.wikipedia.org/wiki/British_Standard_Pipe) — web — Publisher's page; dimensions are facts
- Valves Tubes Fittings: [BS EN 10255 steel tube: nominal bore, OD and wall (light / medium / heavy)](https://www.valvestubesfittings.com/data/pdf/steel-tube/bs-en10255-steel-tube-technical-specifications-weight-dimensions-pressure.pdf) — web — Publisher's page; dimensions are facts
- Engineering ToolBox: [BS 1387 steel tubes: nominal bore, OD and wall (light / medium / heavy)](https://engineeringtoolbox.com/bs1387-steel-tubes-dimensions-d_97.html) — web — Publisher's page; dimensions are facts

## Free STEP/STL (8 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/bsp-taper-pipe-threads-r-rp-iso-7-1/index.json

- R-1-1-4-male-taper-envelope-d41.91: [STEP](https://xemstudio.com/files/hardware/bsp-taper-pipe-threads-r-rp-iso-7-1/R-1-1-4-male-taper-envelope-d41.91.step) · [STL](https://xemstudio.com/files/hardware/bsp-taper-pipe-threads-r-rp-iso-7-1/R-1-1-4-male-taper-envelope-d41.91.stl) — R 1-1/4 male taper (ISO 7-1) envelope: major diameter Ø41.91 at the gauge plane, taper 1:16 down to Ø41.116 at the free end over the gauge length a = 12.7 mm; then an EXAMPLE EN 10255 medium tube stub OD Ø42.4 x 3.25 wall, 30 mm long (our example length); bore Ø35.9 through; the thread is a smooth cone at the major diameter, not helical; the thread runs on past the gauge plane in a real part, only the gauge length is drawn
- R-1-1-2-male-taper-envelope-d47.803: [STEP](https://xemstudio.com/files/hardware/bsp-taper-pipe-threads-r-rp-iso-7-1/R-1-1-2-male-taper-envelope-d47.803.step) · [STL](https://xemstudio.com/files/hardware/bsp-taper-pipe-threads-r-rp-iso-7-1/R-1-1-2-male-taper-envelope-d47.803.stl) — R 1-1/2 male taper (ISO 7-1) envelope: major diameter Ø47.803 at the gauge plane, taper 1:16 down to Ø47.009 at the free end over the gauge length a = 12.7 mm; then an EXAMPLE EN 10255 medium tube stub OD Ø48.3 x 3.25 wall, 30 mm long (our example length); bore Ø41.8 through; the thread is a smooth cone at the major diameter, not helical; the thread runs on past the gauge plane in a real part, only the gauge length is drawn
- R-2-male-taper-envelope-d59.614: [STEP](https://xemstudio.com/files/hardware/bsp-taper-pipe-threads-r-rp-iso-7-1/R-2-male-taper-envelope-d59.614.step) · [STL](https://xemstudio.com/files/hardware/bsp-taper-pipe-threads-r-rp-iso-7-1/R-2-male-taper-envelope-d59.614.stl) — R 2 male taper (ISO 7-1) envelope: major diameter Ø59.614 at the gauge plane, taper 1:16 down to Ø58.620 at the free end over the gauge length a = 15.9 mm; then an EXAMPLE EN 10255 medium tube stub OD Ø60.3 x 3.65 wall, 30 mm long (our example length); bore Ø53 through; the thread is a smooth cone at the major diameter, not helical; the thread runs on past the gauge plane in a real part, only the gauge length is drawn
- R-2-1-2-male-taper-envelope-d75.184: [STEP](https://xemstudio.com/files/hardware/bsp-taper-pipe-threads-r-rp-iso-7-1/R-2-1-2-male-taper-envelope-d75.184.step) · [STL](https://xemstudio.com/files/hardware/bsp-taper-pipe-threads-r-rp-iso-7-1/R-2-1-2-male-taper-envelope-d75.184.stl) — R 2-1/2 male taper (ISO 7-1) envelope: major diameter Ø75.184 at the gauge plane, taper 1:16 down to Ø74.090 at the free end over the gauge length a = 17.5 mm; then an EXAMPLE EN 10255 medium tube stub OD Ø76.1 x 3.65 wall, 30 mm long (our example length); bore Ø68.8 through; the thread is a smooth cone at the major diameter, not helical; the thread runs on past the gauge plane in a real part, only the gauge length is drawn
- R-3-male-taper-envelope-d87.884: [STEP](https://xemstudio.com/files/hardware/bsp-taper-pipe-threads-r-rp-iso-7-1/R-3-male-taper-envelope-d87.884.step) · [STL](https://xemstudio.com/files/hardware/bsp-taper-pipe-threads-r-rp-iso-7-1/R-3-male-taper-envelope-d87.884.stl) — R 3 male taper (ISO 7-1) envelope: major diameter Ø87.884 at the gauge plane, taper 1:16 down to Ø86.597 at the free end over the gauge length a = 20.6 mm; then an EXAMPLE EN 10255 medium tube stub OD Ø88.9 x 4.05 wall, 30 mm long (our example length); bore Ø80.8 through; the thread is a smooth cone at the major diameter, not helical; the thread runs on past the gauge plane in a real part, only the gauge length is drawn
- R-4-male-taper-envelope-d113.03: [STEP](https://xemstudio.com/files/hardware/bsp-taper-pipe-threads-r-rp-iso-7-1/R-4-male-taper-envelope-d113.03.step) · [STL](https://xemstudio.com/files/hardware/bsp-taper-pipe-threads-r-rp-iso-7-1/R-4-male-taper-envelope-d113.03.stl) — R 4 male taper (ISO 7-1) envelope: major diameter Ø113.03 at the gauge plane, taper 1:16 down to Ø111.442 at the free end over the gauge length a = 25.4 mm; then an EXAMPLE EN 10255 medium tube stub OD Ø114.3 x 4.5 wall, 30 mm long (our example length); bore Ø105.3 through; the thread is a smooth cone at the major diameter, not helical; the thread runs on past the gauge plane in a real part, only the gauge length is drawn
- R-5-male-taper-envelope-d138.43: [STEP](https://xemstudio.com/files/hardware/bsp-taper-pipe-threads-r-rp-iso-7-1/R-5-male-taper-envelope-d138.43.step) · [STL](https://xemstudio.com/files/hardware/bsp-taper-pipe-threads-r-rp-iso-7-1/R-5-male-taper-envelope-d138.43.stl) — R 5 male taper (ISO 7-1) envelope: major diameter Ø138.43 at the gauge plane, taper 1:16 down to Ø136.643 at the free end over the gauge length a = 28.6 mm; then an EXAMPLE EN 10255 medium tube stub OD Ø139.7 x 4.85 wall, 30 mm long (our example length); bore Ø130 through; the thread is a smooth cone at the major diameter, not helical; the thread runs on past the gauge plane in a real part, only the gauge length is drawn
- R-6-male-taper-envelope-d163.83: [STEP](https://xemstudio.com/files/hardware/bsp-taper-pipe-threads-r-rp-iso-7-1/R-6-male-taper-envelope-d163.83.step) · [STL](https://xemstudio.com/files/hardware/bsp-taper-pipe-threads-r-rp-iso-7-1/R-6-male-taper-envelope-d163.83.stl) — R 6 male taper (ISO 7-1) envelope: major diameter Ø163.83 at the gauge plane, taper 1:16 down to Ø162.043 at the free end over the gauge length a = 28.6 mm; then an EXAMPLE EN 10255 medium tube stub OD Ø165.1 x 4.85 wall, 30 mm long (our example length); bore Ø155.4 through; the thread is a smooth cone at the major diameter, not helical; the thread runs on past the gauge plane in a real part, only the gauge length is drawn

## Questions

**What is the major diameter of a 1/2 BSPT (R 1/2) thread?**

20.955 mm at the gauge plane, 14 TPI (pitch 1.814 mm), pitch diameter 19.793, minor 18.631, gauge length 8.2 mm.

**What is the major diameter of an R 2 thread?**

59.614 mm, 11 TPI (pitch 2.309 mm), pitch diameter 58.135 mm, gauge length 15.9 mm.

**What is the difference between R, Rp and Rc?**

R is the external taper thread, Rp the internal parallel thread and Rc the internal taper thread (ISO 7-1 designations).

**What is the taper of a BSPT thread?**

1:16 on the diameter: the diameter changes 1 mm for every 16 mm of length.

**How many threads per inch is R 2?**

11 TPI, the same as R 1 to R 6; R 1/2 and R 3/4 are 14 TPI, R 1/4 and R 3/8 are 19 TPI and R 1/16 and R 1/8 are 28 TPI.

## Fits with

- [BSP parallel pipe threads G 1-1/4 to G 6 (ISO 228-1): pitch, major, pitch and minor diameter, class A / B limits + 6 male STEP/STL files](https://xemstudio.com/objects/bsp-parallel-pipe-threads-g-iso-228-1/)
- [NPT male thread envelopes 1/8 to 1 in (ASME B1.20.1)](https://xemstudio.com/objects/npt-thread-envelopes/)
- [NPT pipe thread dimensions (ASME B1.20.1): TPI, E0, E1, L1, L2 and tap drill, NPS 1/8 to 6 + male NPT end STEP/STL](https://xemstudio.com/objects/npt-thread-dimensions-asme-b1-20-1/)
- [ISO 1179 / BSPP (G thread) ports with O-ring or bonded seal: D3, D4, O-ring size, Dowty bonded-seal ID, OD, thickness](https://xemstudio.com/objects/iso-1179-bspp-ports-and-bonded-seals/)
- [NPT pipe plugs: square head, hex head, round head and hex socket (ASME B16.11; Dryseal NPTF, flush PTF) 1/16 to 6 in — head size, length, socket + envelope models](https://xemstudio.com/objects/pipe-plugs-npt-square-hex-socket/)