examples of fittings 
Fittings are used to join two or more pipes, a pipe to a device, or a pipe to a cap or plug.
Threaded fitting with two female ends; it is used to join two pipes of the same diameter.
Fitting joining two pipes of different diameters in order to reduce the diameter of a pipe run.
Fitting with a hexagonal head. It joins two pipes of different diameters: one pipe is screwed onto the male end, and the other into the female end.
Fitting joining two pipes of different diameters. The larger pipe screws onto the male end and the smaller pipe screws into the female end.
square head plug
Cap screwed into the end of a threaded female pipe to close it off.
Plug screwed onto the end of a male threaded pipe to close it off.
Plug inserted into the end of a pipe to close it off.
Threaded fitting having two male ends; it is used to join two pipes of the same diameter.