Why use copper pipe fittings?
Copper is used as it can tolerate very high temperatures and as such, is used widely for central heating applications
Different types of Fittings
Adapters are used to extend runs, or to simply change the connection type at the end of a pipe
Bushings are used to join pipes of different sizes, usually by reducing a larger fitting down to a smaller pipe.
A coupling is used to extend the run of a pipe, or change pipe sizes
If you need to change the direction of flow, elbows are likely your best bet. Produced primarily in 90 and 45 degree angles (unique sizes like 22.5 and 60 are also available), elbows can be threaded or sweated, and are one of the most crucial fittings used in plumbing
When more than one branch is required of a water supply, tees are the way to go. Essentially a long coupling with an outlet on the side, these fittings feature their outlets at 90° from the inlet, and are sized according to their "run" (the horizontal, or straight-through dimension of the fitting), and the side outlet (the "top" of the fitting, 90 degrees off the run). When the run of a tee is smaller than the side outlet, it's often referred to as a "bull head" fitting.
Caps and Plugs
A cap, as its name suggests, is a cap that goes over the end of a pipe, creating a dead end. Plugs also stop up a pipe or tube system, but are plugged, like a stopper, into the end of the pipe.
Cross type Fitting
Cross type fittings contains 4 opening in 4 directions. These are connected when there are 4 pipes are meeting at a point.