NPT: National Pipe Thread Taper, most commonly used in the US
The taper on NPT threads allows them to form a seal when torqued as the flanks of the threads compress against each other, as opposed to parallel/straight thread fittings or compression fittings in which the threads merely hold the pieces together and do not provide the seal.
The thread angle is 60° for NPT threads; NPT threads are flattened at the peaks and valleys.
BSPT thread (or G thread)
BSPT: British Standard Pipe Tapered, Commonly used everywhere but the US
Straight threads with a consistent diameter
Thread angle is 55° for BSPTthreads. Threads are rounded at the peaks and valleys.
BSPP thread (or ZG thread)
BSPP: British standard Pipe Parallel, used in UK and Commonwealth countries.
BSPPM (or R) = External tapered screw pipe thread for fits made on the thread per ISO-7 & BS-21. Per the standard the R mates with the Rc and Rp, but will also mate with the G.
BSPPF (or Rc) = Internal tapered threads for fits made on the thread per ISO-7 & BS-21. Per the standard Rc mates with R.
Thread angle is 55° for BSPP threads. Threads are rounded at the peaks and valleys.
Metric Thread
Most commonly used in China, Australia and Europe
ISO metric screw threads are the world-wide most commonly used type of general-purpose screw thread. MX standards for the thread size (e.g. M20 means the diameter is 20 mm);
