For all over the world, different countries requires different standard of thread for malleable iron pipe fittings.
The main catagery is BSPT, NPT, DIN, and RUSSIA STANDARD .
BSPT means british standard, many countries use it.
NPT means american standard, also used a lot all over the world.
DIN is German standard, which is not used a lot.
Russia standard is only used in some Russia countries.