What Are the Different Types of Pipe Fittings? A Complete Guide

Pipe fittings are components used to connect, redirect, branch, or terminate sections of pipe in a piping system. There are more than a dozen distinct types, each engineered for a specific function — from simple straight couplings to complex multi-outlet manifolds. Choosing the wrong fitting can cause leaks, pressure drops, or outright system failure, so understanding what each type does is essential before any installation or repair.

The most common pipe fittings include elbows, tees, couplings, unions, reducers, caps, plugs, crosses, nipples, flanges, and valves. They are manufactured from materials such as PVC, CPVC, copper, carbon steel, stainless steel, brass, and cast iron — selected based on pressure rating, temperature range, and the fluid being carried.

Elbows — Changing the Direction of Flow

Elbows are among the most frequently used pipe fittings. They redirect the flow of fluid or gas through a pipeline at a specific angle. The two most common configurations are 90° elbows and 45° elbows, though 22.5° versions also exist for more gradual directional changes.

Short Radius vs. Long Radius Elbows

Long radius (LR) elbows have a centerline radius equal to 1.5× the nominal pipe diameter, which produces a smoother flow path with less pressure drop — the preferred choice in most process piping and HVAC systems. Short radius (SR) elbows have a centerline radius equal to the nominal pipe diameter and are used in tight spaces where installation clearance is limited, though they create more turbulence.

• 90° LR elbows: standard in water supply and gas lines
• 45° elbows: used to offset pipes around obstacles with less pressure loss than a 90°
• Street elbows: have one male and one female end, eliminating the need for a separate nipple
• Reducing elbows: change both direction and pipe diameter in a single fitting

Tees — Splitting or Combining Flow

A tee fitting has three openings and is used to split a single pipeline into two branches or to merge two lines into one. Tees come in two primary forms:

• Equal (straight) tees: all three openings are the same diameter — the most common type in residential plumbing
• Reducing tees: the branch outlet is smaller than the run — used when a smaller lateral service line branches off a main supply

In drainage systems, a sanitary tee is specifically designed to direct flow smoothly downward, preventing backflow. Its swept inlet allows waste to enter with less splashing and turbulence compared to a standard tee.

Couplings and Unions — Joining Pipe Sections

Couplings and unions are both used to join two lengths of pipe in a straight line, but they differ critically in how they can be removed.

Couplings

A regular coupling is a permanent joint — once solvent-welded (PVC) or soldered (copper), removal requires cutting the pipe. A slip coupling (also called a repair coupling) has no internal stop, allowing it to slide along the pipe to repair a damaged section without cutting back to a fitting.

Unions

A union consists of three parts — a nut, a female end, and a male end — and creates a joint that can be unscrewed and reconnected without cutting the pipe. Unions are mandatory in any run serving equipment (pumps, water heaters, meters) that will need periodic removal, because they allow the equipment to be disconnected without disturbing the surrounding piping.

Reducers — Changing Pipe Diameter

A reducer connects two pipes of different diameters. There are two types:

• Concentric reducers: both ends share the same centerline — used in vertical pipelines to avoid air pockets or sediment accumulation
• Eccentric reducers: the centerlines are offset — used in horizontal pipelines where the bottom of the pipe must remain flat to prevent cavitation or allow complete drainage

For example, transitioning from a 4-inch main to a 2-inch branch in a hydronic heating system uses an eccentric reducer with the flat side up to prevent air trapping.

Caps and Plugs — Terminating a Pipeline

Caps and plugs both seal the end of a pipe, but they attach differently:

• Caps fit over the outside of a pipe's male end (female socket)
• Plugs insert into the inside of a fitting's female end (male thread)

Both are used to blank off unused outlets, pressure-test a system, or permanently terminate an extension point. Pressure-rated steel caps are required in high-pressure gas or steam systems; PVC caps are common in low-pressure water supply.

Crosses and Wyes — Multi-Directional Flow Control

A cross fitting has four openings — one inlet and three outlets (or any combination) arranged in a plus-sign configuration. Crosses are less common than tees because they create stress at a single point under thermal expansion; they are used primarily in fire sprinkler systems and low-pressure irrigation layouts.

A wye (Y) fitting branches off at a 45° angle rather than 90°. This produces significantly less turbulence than a tee at the branch point and is preferred in drainage, waste, and vent (DWV) systems where smooth flow is critical to preventing clogs.

Nipples — Short Pipe Extensions

A nipple is a short length of pipe, threaded on both ends, used to connect two female-threaded fittings. Types include:

• Close nipples: fully threaded from end to end, no unthreaded center; used when zero separation between fittings is needed
• Hex nipples: have a hex center for wrench gripping — easier to install and remove without pipe damage
• Long nipples: have an unthreaded section in the middle, useful for achieving a specific spacing between two fittings

Flanges — Bolted, Removable Connections

Flanges are flat disc-shaped fittings with bolt holes around the perimeter. Two flanges are bolted face-to-face with a gasket between them to create a sealed, pressure-rated connection that is fully removable. Flanged joints are the standard for large-diameter industrial pipelines (typically 2 inches and above) where maintenance access is required.

Common flange types include weld-neck, slip-on, socket-weld, threaded, lap joint, and blind flanges. ASME pressure-temperature ratings range from Class 150 (low-pressure water) to Class 2500 (high-pressure steam). A Class 300 carbon steel flange, for instance, is rated to approximately 720 psi at 100°F.

Bushings and Adapters — Bridging Thread and Diameter Differences

A bushing is a compact fitting that reduces the size of a female threaded outlet by inserting a male thread of a different size. For example, a 3/4" × 1/2" bushing lets a 1/2" pipe connect to a 3/4" female fitting — without needing a separate reducer.

Adapters change the connection type rather than diameter — for example, a male-threaded NPT to push-fit adapter lets a copper push-connect system transition to a threaded iron fitting. Male adapters (MIP × socket) and female adapters (FIP × socket) are fundamental transition fittings in mixed-material systems.

Comparison of Common Pipe Fitting Types

How to Choose the Right Pipe Fitting

Selecting a pipe fitting depends on five key variables:

1. Function: Are you changing direction, branching, reducing, terminating, or connecting? Each need maps to a specific fitting type.
2. Pipe material and size: Fittings must match the pipe material (copper to copper, PVC to PVC) or use a compatible transition fitting. Size must match the nominal pipe diameter — a ½" fitting will not seal a ¾" pipe.
3. Pressure and temperature rating: A Schedule 40 PVC elbow is rated to 160 psi at 73°F but degrades rapidly above 140°F. High-temperature steam requires rated steel or stainless components.
4. Connection method: Threaded (NPT), solvent-welded, soldered/brazed, push-fit, press-fit, or flanged — each requires different tools and creates different joints.
5. Future maintenance: Any fitting serving equipment that will need removal should be a union or flanged connection, not a permanent joint.

Mismatched materials — such as connecting copper directly to galvanized steel without a dielectric union — will cause galvanic corrosion within 2 to 5 years, leading to premature joint failure and potential water damage.

Specialty Fittings Worth Knowing

Dielectric Unions

Used wherever dissimilar metals meet (e.g., copper tubing to a galvanized steel water heater). An internal plastic or rubber sleeve electrically isolates the two metals, preventing galvanic corrosion.

Compression Fittings

Compression fittings use a ferrule (olive) and nut to create a watertight seal on soft copper, polyethylene, or nylon tubing without soldering. Common in appliance supply lines, refrigerators, and icemakers. They are removable but should not be reused more than once.

Push-Fit (SharkBite-Type) Fittings

Push-fit fittings grab the pipe using internal stainless-steel teeth and an O-ring. They work on copper, CPVC, and PEX without tools and are removable with a disconnect clip. Rated to 200 psi and 200°F for most brands, they are widely used for emergency repairs and accessible locations where soldering is impractical.

Barbed Fittings

Barbed fittings insert into flexible tubing (vinyl, polyethylene, silicone) and are secured with a hose clamp. The barbs grip the inside of the tube as pressure pushes the tubing against them. They are used extensively in irrigation, aquariums, laboratory systems, and low-pressure fluid transfer.