How to recognise an elbow, tee, reducer, coupler and stop-end, and what each one is for.
Recognising the shapes
Plumbing fittings come in a small number of standard shapes, and knowing them by sight is as useful as knowing how they joint.
An elbow is a right-angled bend built into the fitting body, used wherever a pipe run has to change direction, typically by 90 degrees.
A tee has three openings: two in line and one branching off at 90 degrees. It is used to add a branch to a run, feeding another appliance or outlet without breaking the main pipe.
A reducer has one larger opening and one smaller one, and joins two lengths of pipe of different sizes in a straight line.
A coupler has two openings of the same size and simply joins two lengths of pipe together in a straight line, with no change of direction or size.
A stop-end closes and seals a single pipe opening completely, for example to cap a spur left for a future appliance so the system can still hold water and pressure.
Parts that look similar are easy to confuse. A tee and a coupler can look alike at a glance, but a tee always has the third, branching opening; a reducer and a coupler both join pipe in a straight line, but only the reducer changes the pipe size across the joint.