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 1^o47'
• truncation of roots and crests are rounded
• 55^o thread angle
• pitch is measured in threads per inch
• taper is 3/4" per foot or 1 in 16 on the diameter

Reference standards for BS 21 tapered pipe threads are:

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

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