Key Hydraulic Fittings Terms: 2025 and Ongoing Updates

Connection Method

Adapter

An Adapter is a fitting designed to connect two hydraulic components with different end types or sizes, enabling compatibility between hoses, tubes, or ports.

Swivel Adapter

A Swivel Adapter features a rotating connection that allows one end to turn freely relative to the other, reducing hose twist and facilitating installation in tight spaces.

Union Fitting

A Union Fitting is a two-piece connector that joins two tubes or pipes end-to-end, providing easy assembly and disassembly without rotating the connected lines.

Inline Coupling

An Inline Coupling is installed within the hydraulic line to join two sections of hose or tube, often using threaded ends or quick-connect mechanisms for a secure, leak-free connection.

Transition Adapter

A Transition Adapter is used to convert between different connection types or thread standards—such as JIC to NPT or metric to SAE—ensuring proper fit and seal.

Reducing Adapter

A Reducing Adapter connects hydraulic lines of different diameters, stepping down the flow path from a larger to a smaller size while maintaining sealing integrity.

Male-to-Female Connector

A Male-to-Female Connector pairs a male-threaded end with a female-threaded end to link components with complementary threading, ensuring a secure and sealed joint.

Fitting Geometry

45° Elbow

A 45° Elbow changes the direction of the hydraulic line by 45 degrees, providing a smoother flow path and reducing pressure drop compared to sharper angles.

90° Elbow

A 90° Elbow creates a right-angle turn in the hose or tube, allowing routing around obstacles or tight corners where space is limited.

Tee Fitting

A Tee Fitting divides or combines flow by creating a three-way junction, enabling one inlet to feed two outlets or vice versa in a “T” configuration.

Cross Fitting

A Cross Fitting provides four connection ports in a cross shape, used to split flow evenly into three directions or combine flows from three lines into one.

Y-Fitting

A Y-Fitting splits or combines flow at an angle (typically 45° from the main line), offering reduced turbulence compared to a standard tee.

Street Elbow

A Street Elbow combines a male end and a female end in a single fitting, allowing a change of direction without the need for additional adapters.

Street Tee

A Street Tee has one branch with opposite gender threads, enabling a tee junction where one leg connects directly to another fitting without a separate adapter.

Miter Elbow

A Miter Elbow is a precision-cut tube fitting that bends tubing at custom angles (other than standard 45° or 90°) by mitering the tube ends and welding or brazing them together.

Thread & Standard Series

JIC (37° Flare)

The JIC (Joint Industry Council) 37° flare thread (SAE J514/ISO 8434-2) uses a 37° flare on the tube end to seal metal-to-metal against a corresponding flare seat, providing high-pressure leak-tight connections.

NPT (National Pipe Tapered)

NPT threads (ANSI/ASME B1.20.1) are tapered threads that seal by metal-to-metal interference as the male and female threads wedge together, commonly used in North American hydraulic and pneumatic systems.

BSPP (British Standard Parallel Pipe)

BSPP threads (ISO 228-1) are parallel (straight) threads that rely on a bonded seal or O-ring at a shoulder or face seal to prevent leaks, widely used in European and Asian markets.

BSPT (British Standard Pipe Tapered)

BSPT threads (ISO 7-1) are tapered threads similar to NPT but with a different thread form, sealing by thread interference and often requiring thread sealant or tape.

Metric (ISO 6149 / ISO 261)

Metric threads (ISO 6149 for fluid power ports; ISO 261 general metric threads) use a standardized pitch and diameter in millimeters, sealing via bonded O-ring at the port face for high-pressure applications.

ORFS (O-Ring Face Seal)

ORFS fittings (SAE J1453) feature flat sealing surfaces with an O-ring housed in a groove on the male flat face, providing a robust, leak-free seal under high pressure.

SAE O-Ring Boss (ORB)

SAE ORB threads (SAE J1926) are straight threads that seal by compressing an O-ring between the boss and the port, commonly used for low-vibration, demountable connections.

UN/UNF (Unified National / Unified Fine)

UN and UNF threads (ANSI/ASME B1.1) are standardized inch-based threads; UNF’s finer pitch provides better vibration resistance and is occasionally used in hydraulic fittings.

DIN 2353 Tube Fittings

DIN 2353 fittings use metric threads and a two-ferrule compression system, providing reliable, reusable connections for metric tube-to-tube or tube-to-port joints in hydraulic circuits.

ISO 1179 (O-Ring Boss Port)

ISO 1179 defines straight-threaded ports that seal via an O-ring in the port, harmonizing O-ring boss connections across multiple international standards for ease of interchangeability.

SAE Flareless (Bite Type) – 3000 & 6000 PSI

SAE 3000 and 6000 PSI flareless fittings use a split sleeve (bite-type) design that bites into the tube OD to form a seal, eliminating the need for flaring while supporting high-pressure operation.

Sealing Type

O-Ring Seal

An O-Ring Seal uses a circular elastomer ring compressed between two mating surfaces to prevent fluid leakage under pressure, offering simplicity and easy replacement.

Metal-to-Metal Seal

A Metal-to-Metal Seal relies on precisely machined metal surfaces that deform slightly under load to create a leak-tight joint, ideal for high-temperature or abrasive fluids.

Compression Seal

A Compression Seal uses a ferrule or sleeve that compresses onto the tube OD when the nut is tightened, forming both mechanical grip and fluid seal without auxiliary gaskets.

Face Seal

A Face Seal uses a flat sealing surface—often with an O-ring or gasket seated in a groove—to seal between the male face of a fitting and the flat port face on the mating component.

Bonded Seal (Dowty Seal)

A Bonded Seal features an elastomer ring bonded to a metal washer; tightening compresses the elastomer, sealing pressure ports while the metal washer prevents extrusion.

PTFE Seal

A PTFE Seal employs polytetrafluoroethylene material for its high chemical resistance and low friction, sealing aggressive fluids and extreme temperatures without swelling.

Lip Seal

A Lip Seal uses a flexible lip on the inner diameter of the fitting to engage the tube or bore, providing a dynamic seal that tolerates slight movement or misalignment.

Gasket Seal

A Gasket Seal consists of a flat or shaped gasket (rubber, fiber, metal, or composite) placed between flanges or faces to fill imperfections and prevent leaks.

Elastomeric Seal

An Elastomeric Seal is made from rubber-like materials (e.g., NBR, Viton, EPDM) selected for compatibility with hydraulic fluids and temperature ranges, providing resilient sealing.

Spring-Energized Seal

A Spring-Energized Seal incorporates a metallic spring that maintains radial force on a PTFE or elastomeric sealing lip, ensuring consistent seal pressure under variable conditions.

Double-Ring Seal

A Double-Ring Seal uses two concentric rings—often elastomeric—providing redundant sealing barriers for critical applications where leak prevention is paramount.

Quick-Connect & Couplingscoupling

Quick-Disconnect Coupling

A Quick-Disconnect Coupling allows rapid connection and disconnection of hydraulic lines without tools, featuring internal valves that automatically shut off fluid flow when disconnected.

Camlock Coupling (Cam and Groove)

A Camlock Coupling uses cam arms on the female half to lock onto matching grooves on the male half, providing a secure, tool-free connection commonly used in bulk fluid transfer.

Flat-Face Coupling

A Flat-Face Coupling features flush sealing surfaces that minimize fluid loss and air inclusion during connection and disconnection, ideal for mobile equipment where contamination risk is high.

Dry-Break Quick Coupling

A Dry-Break Quick Coupling automatically traps residual fluid in internal chambers when disconnected, preventing spills and contamination of the work environment.

Push-to-Connect Coupling

A Push-to-Connect Coupling secures hose or tube ends simply by pushing them into the fitting body, where internal teeth grip and seal without tools or ferrules.

Self-Sealing Coupling

A Self-Sealing Coupling incorporates internal valves that close upon disconnection, preventing fluid leakage and minimizing air ingress without additional components.

Bayonet Coupling

A Bayonet Coupling locks by inserting the male half into the female half and twisting slightly, engaging locking lugs for a quick, secure connection resistant to vibration.

Multi-Connection (Multiplex) Coupling

A Multi-Connection Coupling bundles multiple hydraulic circuits into a single, combined quick-connect interface, allowing simultaneous connection of several lines with one action.

Interchangeable Series Coupling

An Interchangeable Series Coupling adheres to international standards (e.g., ISO 16028) so different manufacturers’ couplings can mate, ensuring system compatibility across suppliers.

Hose-to-Tube & Hose-to-Pipe Adapters

Hose Barb Adapter

A Hose Barb Adapter has a ridged barb that grips the inside of a flexible hose when clamped, providing a secure connection between hose and fitting without flaring.

Bulkhead Adapter

A Bulkhead Adapter passes through a panel or wall, sealing the port on both sides and allowing a hose or tube to connect through bulkheads or machine enclosures.

Nipple Adapter

A Nipple Adapter features male threads on both ends, often one end matching a hose fitting and the other matching a pipe or tube thread, to join dissimilar components inline.

Hose Tail Adapter

A Hose Tail Adapter has a smooth, tapered tail for inserting into hose and is secured by a clamp or crimp sleeve, simplifying transitions from hose to threaded connections.

Flared Tube Adapter

A Flared Tube Adapter uses a flared tube end (typically 37° or 45°) to mate with a correspondingly flared hose fitting, providing a metal-to-metal seal without additional seals.

Swivel Hose Adapter

A Swivel Hose Adapter incorporates a 360° rotating joint that prevents hose kinking and twisting during movement or vibration in dynamic applications.

Push-Lok Adapter

A Push-Lok Adapter combines a hose barb with a serrated feature and hose clamp compatibility, specifically designed for push-to-connect hose systems without ferrules.

Crimp-On Adapter

A Crimp-On Adapter is permanently attached to a hose by a crimping machine, compressing the ferrule onto the hose for high-pressure applications.

Thru-Wall Hose Connector

A Thru-Wall Hose Connector facilitates hose connections through panels or tanks, featuring seals on both sides to prevent leaks around the mounting hole.

Flange & Manifold Fittings

Flat-Face Flange

A Flat-Face Flange mating surface is completely flat and seals against a gasket compressed between the flange faces, commonly used in low-pressure hydraulic manifolds.

Split Flange

A Split Flange consists of two clamp-style halves that encircle the hose or tube and bolt together around a machined flange face, eliminating the need to slide a flange over the end of the hose.

Stackable Manifold

A Stackable Manifold is a modular block design with standardized ports and mounting dimensions, allowing multiple valve sections to be stacked vertically to form a compact hydraulic control assembly.

SAE 3000 psi Flange

SAE 3000 psi Flanges comply with SAE J518 specifications, featuring four-bolt patterns and flat sealing faces, designed for medium-pressure hydraulic connections.

Cartridge Manifold

A Cartridge Manifold houses individual cartridge valves pressed into threaded cavities in a block, enabling high-density valve integration with minimal plumbing.

DIN Flange (ISO 6162)

DIN Flanges (ISO 6162) provide metric bolt patterns and flat sealing surfaces with O-ring or metal face seals, standardized for 210 bar and 350 bar hydraulic systems.

Modular Manifold

A Modular Manifold uses interchangeable plates or sections that can be arranged in different layouts, supporting custom hydraulic circuit configurations with common porting interfaces.

Sandwich Plate Manifold

A Sandwich Plate Manifold mounts between an electric actuator and a directional control valve, integrating hydraulic and electro-hydraulic functions in a compact assembly.

Bulkhead & Panel Mounts

Bulkhead Fitting

A Bulkhead Fitting secures a hose or tube through a panel or enclosure wall, using a locking nut and seals on each side to prevent leaks and maintain structural integrity.

Panel-Mount Connector

A Panel-Mount Connector is a threaded fitting with a flange or shoulder that creates a sealed connection point on equipment panels, allowing hoses or tubes to be quickly attached and detached.

Through-Wall Joint

A Through-Wall Joint provides a sealed passage for hydraulic lines through machine walls or structural barriers, typically incorporating multiple seals and a locknut for secure installation.

Locknut

A Locknut secures bulkhead and panel fittings in place, tightening against the enclosure wall to clamp the fitting body and compress O-rings or gaskets for a leak-free seal.

O-Ring Gland

An O-Ring Gland is a machined groove in the fitting body or panel that houses an O-ring, ensuring proper compression and sealing when the bulkhead fitting is installed.

Grommet Seal

A Grommet Seal uses a flexible elastomer insert around the tubing or hose to cushion vibrations and provide a secondary barrier against fluid leakage at panel or bulkhead penetrations.

Compression Bulkhead Adapter

A Compression Bulkhead Adapter combines a bulkhead fitting with a compression nut and ferrule, sealing rigid tubing at the panel interface without the need for flaring.

Weld, Socket-Weld & Brazed Fittings

Socket-Weld Fitting

A Socket-Weld Fitting features a recessed area (socket) into which the pipe is inserted before being fillet welded around the top, providing a smooth bore and strong joint for high-pressure lines.

Butt-Weld Fitting

A Butt-Weld Fitting has ends bevelled to match the pipe and is welded in a butt joint, ensuring full penetration welds and minimal flow disruption for critical hydraulic applications.

Silver-Brazed Joint

A Silver-Brazed Joint uses a silver-based filler metal with a lower melting point than the base materials, creating a leak-tight bond without melting the parent metals.

TIG-Welded Tube Joint

A TIG-Welded Tube Joint employs Tungsten Inert Gas welding to fuse tube ends or fittings, offering precise control and clean welds with minimal distortion.

Lap-Joint Flange

A Lap-Joint Flange consists of a stub end welded to the pipe and a loose backing flange that slides over it, simplifying alignment and disassembly of welded systems.

Socket-Joint Tube Fitting

A Socket-Joint Tube Fitting uses a socket-style recess in the fitting body where the tube end is welded, creating a compact, smooth-walled joint ideal for instrumentation lines.

Fillet-Weld Fitting

A Fillet-Weld Fitting is joined by a fillet weld along the seam between the pipe and the fitting, offering a quicker assembly method for lower-pressure hydraulic circuits.

Bevelled-Edge Joint

A Bevelled-Edge Joint prepares the pipe end with an angled cut (bevel) for precise butt-welding, ensuring deep weld penetration and a continuous bore between pipes and fittings.

Specialty Components

Dust Cap

A Dust Cap is a removable cover placed over unused fitting ends to protect threads and sealing surfaces from contamination and damage when lines are not connected.

Dust Plug

A Dust Plug inserts into an open port or hose end, sealing off the opening to prevent ingress of dirt and moisture during maintenance or transport.

Y-Type Strainer

A Y-Type Strainer incorporates a mesh screen within a Y-shaped body to capture debris and protect downstream components from particulate contamination.

Pressure Gauge Port

A Pressure Gauge Port is a dedicated threaded connection on a manifold or line where a pressure gauge or sensor can be fitted to monitor system pressure.

Test Point Coupler

A Test Point Coupler provides a quick-connect interface for pressure testing or sampling hydraulic fluid without depressurizing the entire system.

Check Valve Cartridge

A Check Valve Cartridge is a removable unit inserted into a manifold or block to permit flow in one direction and prevent backflow, ensuring circuit integrity.

Rotary Union

A Rotary Union allows fluid transfer between stationary and rotating components, maintaining a sealed passage for hydraulic media in rotating machinery.

Flow Divider

A Flow Divider is a specialized fitting or valve that splits hydraulic flow into two or more paths in fixed or adjustable ratios for synchronized actuator operation.

Accumulator Port Adapter

An Accumulator Port Adapter connects an external accumulator to the hydraulic circuit, converting port thread types or sizes to match the accumulator’s fittings.

Blanking Plug

A Blanking Plug seals unused ports in manifolds or blocks to prevent leaks and maintain system pressure when certain circuits are not in use.