BSPT: British Standard Pipe Taper -also known as "R" or "Rc" threads

• BSPP: British Standard Pipe Parallel -also known as "G" or "Rp" threads

Both BSPT and BSPP have the same thread angle, shape, and pitch (threads per inch).  However,

• BSPT threads are tapered and BSPP threads are straight (parallel).
• BSP threads have a 55° included angle and have rounded peaks and valleys (this is a Whitworth thread form).

Here are the actual thread dimension data for BSP threads.  The major diameter is a bit smaller than the actual OD of the pipe, and the minor diameter should be very close to what you would measure inside the female threaded end of a fitting.  Note that the Gage Length dimension pertains only to the BSPT (tapered) thread.