Pipe Threads for Tubes and Fittings where Pressuretight joints are made on the Threads - BS 21
BSPT - British Standard Pipe Taper threads & BSP or BSPF - British Standard Pipe Parallel (Straight) threads
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Threads according BSi - British Standard Institute - BS 21 "Specification for pipe threads for tubes and fittings where pressure-tight joints are made on the threads" can be made as
- parallel (straight) threads
- taper threads
Parallel (straight) Threads
BS parallel threads are also referred to as British Gas, British Pipe Parallel or Parallel Fastening Thread.
Common symbols used for the thread: BSP, BSPP, BSSPI, BSPF, BSPG, PS, Rp, G
The BSPP (parallel) male will mate with a BSPP (parallel) female or a female port.
Usually marked: G size ISO
Taper Threads
BS taper threads are also referred to as British Standard Taper Pipe, Pipe Taper or Conical Thread.
Common symbols used for the thread: BSPT, BSPTr, PT, KR, R, Rc
Usually marked: Rc size ISO
Characteristics of BSPT taper threads:
- tapered thread 1o47'
- truncation of roots and crests are rounded
- 55o thread angle
- pitch is measured in threads per inch
- taper is 3/4" per foot or 1 in 16 on the diameter
| Pipe Size (inches) |
Threads per Inch TPI - Pitch |
Major Diameter OD (inches) |
| 1/16" | 28 | 0.304 |
| 1/8" | 28 | 0.383 |
| 1/4" | 19 | 0.518 |
| 3/8" | 19 | 0.656 |
| 1/2" | 14 | 0.825 |
| 5/8" | 14 | 0.902 |
| 3/4" | 14 | 1.041 |
| 7/8" | 14 | 1.189 |
| 1" | 11 | 1.309 |
| 1-1/4" | 11 | 1.650 |
| 1-1/2" | 11 | 1.882 |
| 1-3/4" | 11 | 2.116 |
| 2" | 11 | 2.347 |
| 2-1/4" | 11 | 2.587 |
| 2-1/2" | 11 | 2.960 |
| 3" | 11 | 3.460 |
Reference standards for BS 21 tapered pipe threads are:
- ISO 7/1
- DIN 2999 - Germany
- JIS B 0203 - Japan
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Related Topics
- Dimensions - Sizes and dimensions of pipes and tubes, and their fittings - inside and outside diameter, weight and more
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Related Documents
- Pipe Threads where Pressuretight Joints are made on the Threads - ISO 7-1 - ISO 7-1:1994 Pipe threads where pressure-tight joints are made on the threads
- Thread Standards - Piping - Piping thread standards
- Threads - Metric ISO 724 - M Thread (metric ISO 724 thread) Standard in Europe
