BSPT = British Standard Pipe Taper

BSPT is an obsolete screw thread designation which is still in common usage. It has been replaced with the R-Series designations. What was BSPT screw thread is now R-Series screw thread with no major physical diferences.

The screw thread is defined in at least two places: BS-21 and ISO-7. These two screw thread standards, as they relate to the product screw threads are technically equilivent.

The R-Series of threads includes:
R = external tapered thread for fits made on the thread per ISO-7 & BS-21.
Rc = internal tapered threads for fits made on the thread per ISO-7 & BS-21.
Rp = internal parallel thread for fits made on the thread per ISO-7 & BS-21
Rs = external parallel thread for fits made on machined face per BS-21 Appendix C.

BS-21 and ISO-7 as they relate to the screw thread gages have diferences. The diferences are for the most part minor and will only result in variation between types at the edge of the product tolerances.

Comments about the above statement can be sent to: gageguy@gagecrib.com