BSP thread dimensions
A pipe’s nominal size is not its physical thread diameter. Check the prefix as well as the size: G, R, Rp and Rc represent different thread forms and roles.
All four 1/4 designations in this catalogue sit at a basic diameter of 13.157 mm. Their shared position does not make them interchangeable. G and R have no tapping recommendation in this release.
G · parallel
G uses parallel-thread dimensions associated with ISO 228.
| Designation / TPI | Basic Ø Parallel · mm | Tap drill mm |
|---|---|---|
| G 1/828 TPI | 9.728 | Not listed |
| G 1/419 TPI | 13.157 | Not listed |
| G 3/819 TPI | 16.662 | Not listed |
| G 1/214 TPI | 20.955 | Not listed |
| G 3/414 TPI | 26.441 | Not listed |
| G 111 TPI | 33.249 | Not listed |
| G 1 1/411 TPI | 41.91 | Not listed |
| G 1 1/211 TPI | 47.803 | Not listed |
| G 211 TPI | 59.614 | Not listed |
Rp · parallel
Rp identifies an internal parallel pipe thread in the ISO 7 family.
| Designation / TPI | Basic Ø Parallel · mm | Tap drill mm |
|---|---|---|
| Rp 1/828 TPI | 9.728 | 8.6 |
| Rp 1/419 TPI | 13.157 | 11.5 |
| Rp 3/819 TPI | 16.662 | 15 |
| Rp 1/214 TPI | 20.955 | 18.5 |
| Rp 3/414 TPI | 26.441 | 24 |
| Rp 111 TPI | 33.249 | 30.2 |
| Rp 1 1/411 TPI | 41.91 | 39 |
| Rp 1 1/211 TPI | 47.803 | 45 |
| Rp 211 TPI | 59.614 | 56.4 |
Rc · tapered
Rc identifies an internal tapered pipe thread. The recommendation shown is the source’s “drill only” value. The taper is 1:16.
| Designation / TPI | Basic Ø At gauge plane · mm | Tap drill mm |
|---|---|---|
| Rc 1/828 TPI | 9.728 | 8.4 |
| Rc 1/419 TPI | 13.157 | 11.2 |
| Rc 3/819 TPI | 16.662 | 14.75 |
| Rc 1/214 TPI | 20.955 | 18.25 |
| Rc 3/414 TPI | 26.441 | 23.75 |
| Rc 111 TPI | 33.249 | 30 |
| Rc 1 1/411 TPI | 41.91 | 38.5 |
| Rc 1 1/211 TPI | 47.803 | 44.5 |
| Rc 211 TPI | 59.614 | 56 |
R · tapered
R identifies an external tapered pipe thread. Dimensions here are basic diameters at the gauge plane. The taper is 1:16.
| Designation / TPI | Basic Ø At gauge plane · mm | Tap drill mm |
|---|---|---|
| R 1/828 TPI | 9.728 | Not listed |
| R 1/419 TPI | 13.157 | Not listed |
| R 3/819 TPI | 16.662 | Not listed |
| R 1/214 TPI | 20.955 | Not listed |
| R 3/414 TPI | 26.441 | Not listed |
| R 111 TPI | 33.249 | Not listed |
| R 1 1/411 TPI | 41.91 | Not listed |
| R 1 1/211 TPI | 47.803 | Not listed |
| R 211 TPI | 59.614 | Not listed |
Recommendations vary with material, engagement and tool. These values are transcribed from the Alpha / Sterling chart, not calculated by subtracting pitch. They are not intended for forming taps. A nearby catalogue drill is a dimensional comparison, not a substitute recommendation.
Sources & scope
Data edition 1.0. Values come from the reference sources below. SizeAxis is a selected reference catalogue; it does not certify manufactured dimensions or thread compatibility.
Read the measurement definitions and full coverage