BSPT

• British Standard Pipe Tapered thread, diameter increases or decreases along the length of the thread.This is more popular type of thread fitting in China and Japan. Thread sealant is needed to seal the male and female fitting together.
• Threads are taper external, parallel internal or taper internal and are intended for use with pipes suitable for threading and for valves, fittings or other pipeline equipment interconnected by threaded joints.
• An appropriate jointing medium should be used on the thread to ensure pressure-tight joints.
• ISO 7-2 gives details of methods of verification of jointing thread dimensions and form and recommended gauging systems.
• The symbols for pipe thread type: Rp - Parallel internal threads, Rc - taper (conical) internal threads, R - external threads
• Designation: Internal thread - Parallel: Pipe thread ISO 7-Rp 1/2, Internal Thread - Taper: Pipe thread ISO 7- Rc 1/2, External thread - Always taper: Pipe thread ISO 7 - R ½
• The ISO 7-1 thread shall be a right-hand thread unless otherwise specified.
• The basic form of the parallel and taper pipe thread shall be as shown in following figures. The taper is 1 to 16, measured on the diameter.

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References

1. http://www.ralstoninst.com/news/story/the-difference-between-npt-bspp-and-bspt-seals
2. ISO 7-1:2000 Pipe Threads Where Pressure-Tight Joints are Made on the Threads - Dimensions, Tolerances and Designation
3. http://www.amesweb.info/Screws/BSPT-Thread-Sizes-Dimensions.aspx