Piping and plumbing fittings

Piping and plumbing fittings

"Fittings" are used in pipe and plumbing systems to connect straight pipe or tubing sections, to adapt to different sizes or shapes, and to regulate fluid flow, for example. Fittings, especially noncommon types, can be expensive, and require time, materials, and tools to install, so they are a non-trivial part of piping and plumbing systems. Valves are technically fittings, but are usually discussed separately.

Materials for fittings

The 'bodies' of fittings for pipe and tubing are most often of the same base material as the pipe or tubing being connected, e.g., copper, steel, polyvinyl chloride (PVC), or other plastic. However, any material that is allowed by code may be used, but must be compatible with the other materials in the system, the fluids being transported, and the temperatures and pressures inside and outside of the system. For example, brass-bodied fittings are common in otherwise copper piping and plumbing systems. Fire hazards, earthquakes, and other factors also influence fitting materials.

Common fittings for both piping and plumbing

While there are hundreds of specialized fittings manufactured, some fittings are used widely in piping and plumbing systems.


A pipe fitting installed between two lengths of pipe or tube allowing a change of direction, usually 90° or 45°. The ends may be machined for butt welding, threaded (usually female), or socketed, etc. When the two ends differ in size, it is called a reducing or reducer elbow.

Most elbows are available in short radius or long radius of types. The short radius elbows have a center to end distance equal to the NPS in inches, while the long radius is 1.5 times the NPS in inches. Short elbows are universally available; long elbows are readily available in Acrylonitrile butadiene styrene (ABS, plastic), PVC for DWV, sewage and central vacuums, and copper for 1950s to 1960s houses with copper drains.

treet elbow

A variant of the elbow, typically of male to female connections; see Street elbow.


A tee is used to either combine or split a fluid flow. Most common are tees with the same inlet and outlet sizes, but 'reducing' tees are available as well. Tee-fittings are also an integral part of the computer-enthusiast level watercooling solutions found in many modern enthusiast PCs.The fitting is one of the three main components of a T-Line, alongside an end-cap or fillport and a length of tubing.They are plumbed into the system, with the perpendicular barb (and its attached stretch of tubing leading to a fillport or a cap).


A cross has one inlet and three outlets, or vice versa. Crosses are common in fire sprinkler systems, but not in plumbing due to their extra cost as compared to using two tees.

The three outlets should be named in order; left, middle , right. For example 15-22-15


A coupling connects two pipes to each other. If the material and size of the pipe are not the same, the fitting may be called a 'reducing coupling' or reducer, or an adapter. The term 'expander' is not used for a coupler that increases pipe size; instead 'reducer' is used.

Couplings for copper pipe are available either with or without a stop. The stop is in the center of the coupling and is useful for ensuring that the coupling is centered between the two pipes being connected. The disadvantage of a stopped coupling is that in some repair situations it may be necessary to slide the coupling completely on to one pipe and then slide it back when the pipes being joined are in position. The type of coupling that doesn't have a stop is referred to as a repair coupling. Repair couplings are available in longer than standard lengths to facilitate the repair of a short length of pipe.


A type of pipe fitting, often liquid or gas tight, which covers the end of a pipe. A cap has a similar function to a plug. In plumbing systems that use threads the cap has female threads.


A plug closes off the end of a pipe. It is similar to a cap but it fits inside the fitting it is mated to. In a threaded iron pipe plumbing system, plugs have male threads.


A union is similar to a coupling, except it is designed to allow quick and convenient disconnection of pipes for maintenance or fixture replacement. While a coupling would require either solvent welding or being able to rotate all the pipes adjacent as with a threaded coupling, a union provides a simple nut transition, allowing easy release at any time.

In addition to a standard union, there exist dielectric unions which are used to separate dissimilar metals (such as copper and galvanized steel) to avoid the damaging effects of electrolysis. When two dissimilar metals are placed in an acidic solution (most tap water is mildly acidic), they will form a battery and generate a voltage. If the two metals touch and conduct, the current from one metal to the other will cause a movement of ions from one to the other, dissolving one metal and depositing it on the other ("galvanic action"). A dielectric union breaks the electric current with a plastic liner between two halves of the union, thus limiting corrosion due to galvanic action.


Short stub of pipe, usually threaded iron, brass or copper; occasionally just bare copper. A nipple is defined as being a short stub of pipe which has two male ends.

Additional common fittings for plumbing systems

Closet flange

The closet flange is the drain pipe flange to which a 'water closet' (toilet) is attached.


Clean-outs are fittings that allow access to drains without removing plumbing fixtures. They are used for allowing an 'auger' or 'plumber's snake' to 'clean out' a plugged drain. Clean-outs should be placed in accessible locations throughout a drainage system, and outside the building as these augers have limited length. The minimum is typically at the end of each branch, just ahead of each water closet, at the base of each stack, and both inside and outside the building in the building drain/sewer. Clean-outs normally have screw-on caps.

Trap primers

Trap primers regularly inject water into traps so that "water seals" are maintained. This seal is necessary to keep sewer gases out of buildings.


A combination tee (combo tee) is a tee with a gradually curving center connecting joint. It's used in drain systems to provide a smooth, gradually curving path to reduce the likelihood of clogs and to ease pushing a plumber's snake through a drain system. The "combo" is a combination of a wye and a 1/8 bend or 45° elbow.

anitary Tee

A sanitary tee is a tee with a curved center section designed to minimize the possibility of siphon action that could draw water out of a trap. The center connection is generally connected to the pipe which leads to a trap (the trap arm).

Double Sanitary Tee (Sanitary Cross)

Similar to a cross. This fitting differs from a standard cross in that two of the ports have curved inlets. The fitting has been used in the past for connecting the drains of back to back fixtures (such as back to back bathroom sinks). Some current codes (including the 2006 UPC) preclude the use of this fitting for that purpose. Instead a Double Fixture Fitting is required.

Y Piece

A type of waste fitting tee which has the side inlet pipe entering at a 45° angle.

Hydraulic fittings

Hydraulics use extremely high fluid pressures to create useful work, such as in the actuators for machinery such as backhoes. As such the hydraulic fittings are designed and rated for much greater pressures than those experienced in general piping systems and they are generally not compatible for use in general plumbing. More information on hydraulics and their fittings can be found in the hydraulic machinery article.

ee also

*Water supply systems
*Traps, Drains, and Vents
*Rainwater, surface, and subsurface water drainage
*Septic systems
*Fuel gas, steam, and other piping


External Resources

* [http://www.iapmo.org/ the International Association of Plumbing and Mechanical Officials]
* [http://www.iccsafe.org/ the International Code Council]
* [http://www.astm.org/ the American Society for Testing and Materials]
* [http://www.spedweb.com Society of Piping Engineers and Designers] (Society of piping professionals with many resources and technical information)

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