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

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)
Pitch (mm) Major Diameter (mm) Minor Diameter (mm)
1/16" 28 0.304 0.907 7.723 6.561
1/8" 28 0.383 0.907 9.728 8.566
1/4" 19 0.518 1.337 13.157 11.445
3/8" 19 0.656 1.337 16.662 14.950
1/2" 14 0.825 1.814 20.955 18.631
5/8" 14 0.902 1.814 22.911 20.587
3/4" 14 1.041 1.814 26.441 24.117
7/8" 14 1.189 1.814 30.201 27.877
1" 11 1.309 2.309 33.249 30.291
1-1/8" 11 1.49 2.309 37.897 34.939
1-1/4" 11 1.650 2.309 41.910 38.952
1-1/2" 11 1.882 2.309 47.803 44.845
1-3/4" 11 2.116 2.309 53.746 50.788
2" 11 2.347 2.309 59.614 56.656
2-1/4" 11 2.587 2.309 65.710 62.752
2-1/2" 11 2.960 2.309 75.189 72.226
3" 11 3.460 2.309 87.844 84.926

Reference standards for BS 21 tapered pipe threads are:

  • ISO 7/1
  • DIN 2999 - Germany
  • JIS B 0203 - Japan

Related Topics

  • Dimensions - Sizes and dimensions of pipes and tubes, and their fittings - inside and outside diameter, weight and more

Related Documents

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