BSPT Pipe Thread
Pipe Threads · 7 specs
Direct Answer
BSPT (British Standard Pipe Taper), designated as the 'R' series under ISO 7-1 and EN 10226, is a 55° Whitworth pipe thread with a 1:16 taper rate. Commonly used in European, Commonwealth, and Japanese plumbing systems, external tapered R threads mate with either internal parallel Rp threads or internal tapered Rc threads to achieve pressure-tight joint sealing.
Source: ISO 7-1:1994 (EN 10226-1 / BS 21) · Last reviewed Aug 28, 2026
Specs
| Standard Governing Body | ISO 7-1 / EN 10226-1 / BS 21 / DIN 2999 |
| Thread Designation | R (Male taper), Rc (Female taper), Rp (Female parallel) |
| Thread Form & Flank Angle | 55° Whitworth with radiused crests and roots |
| Taper Ratio | 1:16 (0.75 in/ft or 1° 47' with centerline) |
| Common Pitches (TPI) | R 1/8": 28 TPI | R 1/4"-3/8": 19 TPI | R 1/2"-3/4": 14 TPI | R 1"-2": 11 TPI |
| Sealing Mechanism | Metal-to-metal flank wedging + jointing paste/PTFE tape |
| Primary Geographical Region | Europe, United Kingdom, Japan (JIS B 0203), Commonwealth |
The ISO 7-1 R, Rc, and Rp System
The ISO 7-1 standard specifies three distinct thread types that work together:
- R (External Taper): Male pipe thread cut on a 1:16 taper with 55° Whitworth geometry.
- Rc (Internal Taper): Female pipe thread cut on a matching 1:16 taper for heavy industrial high-pressure pipework.
- Rp (Internal Parallel): Female cylindrical thread (often called BSPP with thread-sealing capability) that allows a tapered R male fitting to screw in until flank interference creates a seal.
BSPT vs NPT Distinction
While both BSPT and NPT share an identical 1:16 taper rate (0.75 in/ft), they differ in two critical dimensions:
- Flank Angle: BSPT is 55° with radiused roots/crests; NPT is 60° with flattened (truncated) roots/crests.
- Pitch (TPI): 1/2" and 3/4" sizes happen to share 14 TPI, but 1/8" (28 vs 27 TPI), 1/4" (19 vs 18 TPI), and 1" (11 vs 11.5 TPI) have incompatible pitches and will strip if forced.