Pipe fittings connect pipe sections, change direction, create branches, change size or close an opening. Common types include elbows, tees, crosses, couplings, unions, reducers, bushings, nipples, adapters, caps, plugs and flanges. This guide explains these 12 fitting families and how to tell them apart.
Choose the shape for the job, then identify the connections at every end. A female-threaded 90° elbow and a butt-weld 90° elbow make the same turn, but they connect to the pipe in different ways.
12 Common Pipe Fitting Types at a Glance
These are common families rather than an exhaustive classification. Names can overlap: a reducing adapter changes both size and connection type.
Fittings That Change Direction or Create Branches
Elbows
An elbow turns a pipe run. Common angles are 45° and 90°. A street elbow has a male end and a female end, allowing a direct connection where an ordinary female-threaded elbow would need a nipple.
For standard butt-weld elbows, long-radius and short-radius forms are commonly described as 1.5D and 1D, with D referring to nominal pipe size. For example, an NPS 4 long-radius 90° elbow has a nominal center-to-end dimension of 6 inches. This example applies to the 90° form; use the applicable dimensional table or drawing for other angles and constructions.
Tees and crosses
An equal tee has the same nominal size at all three ends. A reducing tee has at least one smaller end. For a reducing tee, label the two run connections and the branch on a sketch. In the common run × run × branch convention, a 1 × 1 × 1/2 tee has 1-inch run ends and a 1/2-inch branch. Suppliers sometimes list sizes in a different order, so state the convention when you place the order.
A cross connects four openings in one body. Its compact layout still needs clearance for assembly and suitable pipe supports. A wye provides an angled branch and is common in drainage layouts. A welded branch outlet connects through a prepared opening in the run pipe; it serves a different installation arrangement from a full tee.
LILY’s nickel-plated brass tee with 1/2-inch BSPP female connections (JEJBNBED) provides a concrete example. Both the nominal size and the thread standard belong in the order description.
Fittings That Join Pipe Sections
Couplings and unions
A conventional threaded coupling joins two pipe ends, but disassembly usually requires rotating a pipe section or releasing an adjacent connection. Grooved and other mechanical couplings have different assembly arrangements.
A union separates at its union assembly. This makes it useful beside a pump, filter or other component that may need removal. Leave room to reach the nut and separate the joint. Match the seat or gasket material to the fluid and temperature.
Nipples and adapters
A pipe nipple is a short length of pipe, commonly with male threads at both ends. Overall length matters because the engaged threads consume part of that length. A close nipple has little or no unthreaded barrel available for a wrench; choose its length and installation method for the available space.
LILY’s fully threaded 316/316L stainless steel nipple (EEHFKBG) is listed with 1-inch NPT male connections, a 1.5-inch overall length and Schedule 80 wall designation.
An adapter changes the connection interface. Describe both ends: for example, “1/2-inch NPT male × compression connection for 1/2-inch OD tube.” The tube connection system and material must also be specified. Tube OD and nominal pipe size use different sizing conventions.
Flanges
A flange forms part of a bolted joint. Match its standard, size, pressure class and facing, then select compatible gaskets and bolting. A threaded flange has a threaded pipe connection and a separate flanged mating face; those two interfaces seal differently.
A blind flange closes a flanged opening. Other flange constructions connect the pipe to equipment or another pipe section. ASME B16.5 covers pipe flanges and flanged fittings from NPS 1/2 through NPS 24, subject to the types and classes within its scope.
Fittings That Change Size or Close an Opening
Reducers and reducing bushings
A concentric reducer keeps the pipe centerlines aligned. An eccentric reducer offsets the centerlines while keeping one side of the transition straight. That offset can help manage air pockets or drainage, depending on the line layout.
On many horizontal liquid-pump suction arrangements, an eccentric reducer is installed flat side up to avoid trapping air at the top. A flat-side-down orientation can keep the pipe bottoms aligned where drainage is required. Select the orientation from the actual piping layout and equipment instructions.
A threaded reducing bushing has a larger male thread outside and a smaller female thread inside. It screws into a larger female opening to accept a smaller male connection. A reducing coupling offers another way to connect different sizes, with a different end arrangement and installation length.
Caps and plugs
A threaded cap fits over a male pipe end; a threaded plug screws into a female opening. A butt-weld cap closes a prepared pipe end. Choose the closure by its connection and rating, then check access for the installation tool.
Plug heads may be hex, square or recessed socket designs. A recessed head can reduce protrusion, but the tool still needs a clear path to engage it.
Fitting Shape and Connection Method Are Separate Choices
Threaded fittings may use tapered or parallel threads. NPT, BSPT and BSPP are different specifications. Make sure both parts use the same thread standard, and follow the manufacturer’s sealing instructions for the complete connection.
Unthreaded ends vary by product. For iron and steel unthreaded pipe and fittings, identify the plain-end, weld-end or flanged design before selecting mating components.
Iron and steel clamp-on pipe and fittings use a clamping connection for assembly without threading or welding.
Common Pipe Fitting Materials
Compare brass and bronze threaded fittings with brass and bronze unthreaded pipe and fittings. The product specifications identify the alloy and end connections. For drinking-water service, verify the required product approvals as well as alloy composition.
Our range includes stainless steel threaded pipe and fittings and stainless steel unthreaded pipe and fittings. Compare the specified grade and joint design for your fluid and cleaning requirements.
Our pipe fittings catalog groups products by material and connection family. Start with the fitting’s function, then use the relevant product category to compare specifications.
The steel and iron threaded catalog is organized into pressure categories: low-pressure iron and steel threaded fittings, medium-pressure iron and steel threaded fittings, high-pressure iron and steel threaded fittings and extreme-pressure steel threaded fittings. These are catalog groupings, not interchangeable pressure ratings.
Pipe collars are related accessories outside the 12 fitting families described here; this category lists two-piece clamp-on designs.How to Specify the Right Pipe Fitting
Function and geometry. Identify the turn, branch, transition or closure, including elbow angle or reducer arrangement.
Every end connection. Record its size, standard, connection method and male or female thread where applicable.
Installation dimensions. Include center-to-end dimensions, overall length and space for tools or joint separation.
Material and service. State the fluid, operating temperature, pressure and relevant corrosion conditions.
Rating and governing requirements. Read the component’s rating at the service temperature and apply the requirements of the applicable piping code.
For illustration, a purchasing description could read: “Elbow, 90°, 1/2-inch NPT female × female, forged carbon steel to ASTM A105, Class 3000, ASME B16.11.” This example shows the specification format; it does not identify a particular catalog item.
Class 3000 is a rating designation, not a pressure in psi. In ASME B16.11, threaded fittings are designated Class 2000, 3000 and 6000, and socket-weld fittings Class 3000, 6000 and 9000. The available classes depend on the fitting type and size. Determine the allowable service pressure from the applicable standard and product documentation for the material and temperature. Pipe schedule identifies a wall-thickness series; assess the complete joint, including the fitting, pipe and sealing components.
For example, NPS 1/2 pipe has a standard outside diameter of 0.840 inch (21.3 mm, rounded). A 1/2 NPT thread has 14 threads per inch. The pipe-body OD is a reference dimension; the measured diameter along an NPT taper varies with the measurement position.
For dimensional checks, see how to measure pipe size. For NPT nominal sizes and threads per inch, use the NPT thread chart.
The governing code depends on the system and jurisdiction. Process piping is often covered by ASME B31.3 and power piping by ASME B31.1; building plumbing and fuel-gas systems follow the applicable local codes. If you are unsure which code applies, ask the engineer of record.
FAQ
Can I replace one 90° elbow with two 45° elbows?
Possibly. Two 45° elbows oriented in the same plane can make a 90° turn, but their combined center-to-end dimensions differ from those of one 90° elbow. The replacement also adds a joint. The pair must fit between the existing connection points, leave room for tools, and meet the line’s support and flow requirements.
Are stainless steel pipe fittings automatically sanitary fittings?
No. Hygienic service depends on the joint design, surface finish, cleanability and other application requirements. A conventional threaded fitting does not become a sanitary fitting simply because it is made from 304 or 316 stainless steel.
Can I mix union halves from different manufacturers?
Use only a combination documented as compatible. The union nut threads, seat geometry and sealing parts must work together as one assembly. When replacing an unidentified union, choose a complete compatible assembly rather than pairing an old half with an unverified replacement.
Technical Reference
ASME B16.11 — Forged Fittings, Socket-Welding and Threaded covers forged socket-weld and threaded fittings. ASME B16.9 addresses factory-made wrought butt-welding fittings, ASME B16.5 addresses pipe flanges and flanged fittings, and ASME B1.20.1 addresses general-purpose inch pipe threads.
Need Help Matching a Fitting?
To check a replacement or request a fitting, contact us with a labeled sketch, photographs, end specifications and operating conditions.
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