For the material of carbon steel pipe fittings, there are some threaded types of fittings.
BARREL NIPPLE: another name is long nipple, it is produced by cutting pipes and process with threading. The length can be customized, the usage is for connecting.
KIM NIPPLE: some buyer call it king nipple, one side connects with socket, another side connects with soft pipes.
SOCKET/COUPLING: it is very useful in construction, both sides are female thread, it can connect 2 pipes together.
HOSE NIPPLE: both side can be connect with soft pipe.