There are a few different thread types out there. They are not necessarily interchangeable, and some uses two different names.
The most common thread standards are:
- BSP - British Standard Pipe
- NPT - National Pipe Thread
- M - Metric threads
BSP exists in two types, BSPP and BSPT. The last letter indicates the shape of the threads.
- BSPP - Parallel
- BSPT - Tapered
Sometimes different names are used for the same thread type. As an example, a 1/2" BSPP can be sold as G1/2". Similarly a 1/2" BSPT can be sold as R1/2".
The picture below illustrates all of this. As you can see, a BSPT male thread will mate with both a BSPP and BSPT female thread.