Plumbing fittings come in all shapes and sizes, with each individual type being used for a specific purpose. Joints or elbows are commonly used, as well as tee and cross fittings. Most plumbing fittings are used to change the direction of the water's flow or to stop it altogether.
Elbow joints are plumbing fittings that are used to change the direction of the water's flow to either a 45° or 90° angle. They are commonly used under sinks and other fixtures in which a drain is used to better regulate the speed at which the water exits the fixture and enters the septic or sewer system. Elbow ends may be socketed, butt welded, or threaded. A street elbow is a variation of this type of fitting, generally using male to female threads.
The tee joint is another type of plumbing fitting, used primarily to combine or divide a flow of water. Both ends are generally the same size, although there are varieties available that have differing inlet and outlet sizes, also known as a reducer joint. Tee joints can also be used in certain computer components.
Cross joints are also plumbing fittings. They have three inlet valves and one outlet valve or vice versa, and are commonly used for sprinkler systems. Often, they are not used when adding plumbing to a home because they are more expensive than using multiple tee joints.
Plumbing fittings are not always joints. This is the case with caps and plugs, both of which are used for closing off the end of a pipe. The difference between the two is in the way each fitting is designed. Caps fit over the ends of a pipe, generally being threaded so they screw in. Plugs fit into the end of a pipe. Both are generally gas and water tight.
Clean-outs are also plumbing fittings that are used on a temporary basis. They are installed in an easily accessible area to allow an auger or pipe snake to be inserted to clean out clogged areas of piping. After the pipes are cleaned, the clean-outs are typically removed.
Most plumbing fittings are made from various types of plastic or metal, most commonly polyvinyl chloride (PVC). Copper and other metal fittings may also be available for older homes which may have copper drains. Fittings are generally sold in home improvement and plumbing supply centers, and are installed using specialized plumbing glues and adhesives.