examples of fittings [2]
Fittings are used to join two or more pipes, a pipe to a device, or a pipe to a cap or plug.
pipe coupling 
Threaded fitting with two female ends; it is used to join two pipes of the same diameter.
reducing coupling 
Fitting joining two pipes of different diameters in order to reduce the diameter of a pipe run.
hexagon bushing 
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.
flush bushing 
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.
threaded cap 
Plug screwed onto the end of a male threaded pipe to close it off.
cap 
Plug inserted into the end of a pipe to close it off.
nipple 
Threaded fitting having two male ends; it is used to join two pipes of the same diameter.