What threads are used for plumbing?

The standard for pipe threads is called NPT which is the short form for national pipe thread and includes many different types of threads such as NPT, NPS and NPTR and many others. The hemet plumbers use these threads in processes of plumbing.

National pipe taper:

NPT stands for national pipe taper and NPS stands for national pipe straight and they both have their own uses in the plumbing world. The tapered threads are in fact tapered or slightly conical meaning that if we would continue these lines they would eventually meet up down the line as opposed to straight threads which are parallel to each other and would never meet. They are also different because the tapered threads have tapered female threads and the straight threads have straight female threads.

How they actually seal?

The part at the beginning of the thread is the root. Next to inside of the root we have the Crest and the part where there is slant is  the flank. We could see that they use the actual threads themselves to create a seal due to the flanks on both the pipe and fitting compressing against each other when their fixed in it. This compression creates a lot of resistance as it is being tightened and to aid the threads to go in all the way and fully seat, the PTFE tape or the Teflon tape is used around the threads which is most commonly used by the hemet plumbers. Teflon is known for its non stick and frictionless surface. So, it helps a lot at getting this task done. This tape is also used to seal to some extent but it's not its primary purpose as many tend to believe a better option for sealing would be to use a thread and paste. Thread which is used more in the UK and neighbouring countries actually expands when it comes in contact with liquid or moisture so it is better at sealing but not as good for fighting friction and it takes a lot longer to install.