Hydraulic hose and fitting terms. Defined the way the counter uses them.

A fitting that joins two connections, usually of different types or sizes — a JIC male to an NPT male, say. Unlike a hose end, it has no hose tail.

A straight-thread port end (ORB, ORFS or metric O-ring) with a locknut and backup washer, so an elbow or tee can be turned to face the right way before the nut is tightened. Rated below the fixed version of the same end.

The aerospace 37° flare fitting. It shares its seat angle and thread with JIC, but is made to tighter tolerances; JIC parts should not be substituted into AN systems.

A ring-shaped fitting held to a port by a hollow bolt, with a seal washer either side. It turns the flow through 90° in very little space.

The tightest radius a hose may be bent to in service, measured to the inside of the bend. Bending tighter shortens hose life sharply; the figure is printed in the hose datasheet for each size.

A compression fitting for plain-end tube in which a ring or sleeve bites into the tube wall as the nut is made up. DIN 2353 (now ISO 8434-1) and SAE flareless fittings both work this way.

A steel washer with a rubber ring bonded to its bore, used to seal parallel threads such as BSPP and metric on a flat port face. Often called a Dowty washer. Use a new one every time.

British Standard Pipe Parallel, ISO 228-1, written G1/2 and so on. A 55° parallel thread that does not seal on the thread: it needs a bonded washer, an O-ring or a 60° cone in a female swivel.

British Standard Pipe Taper, ISO 7-1, written R1/2 for the male and Rc1/2 for the female. Same pitch and diameter as BSPP, but tapered, so it seals on the thread. It does not interchange with NPT.

A fitting with a long threaded body that passes through a panel or tank wall and is clamped either side by a locknut.

The pressure at which a hose or fitting fails in a test. Never a working figure: hydraulic hose is rated so that working pressure is a quarter of minimum burst.

The two pressure classes of SAE J518 four-bolt flange. Code 61 is standard pressure, Code 62 high pressure, with a thicker head and wider bolt spacing at the same size. They do not interchange.

Hose built to a smaller outside diameter and tighter bend radius than the standard grade at the same pressure — SAE 100R16, R17 and the EN 857 1SC/2SC types.

The angled sealing face a flared or swivel fitting seals on. The angle names the family: 37° JIC, 45° SAE, 30° JIS and Komatsu, 24° DIN, 60° BSP. Different angles never seal on each other.

The outside diameter of a ferrule after crimping, measured with calipers halfway between the die ridges. It is set for one maker’s hose in that maker’s fitting series, and is the check that a crimp is right.

Permanently attaching a hose fitting by squeezing its ferrule onto the hose in a set of dies, to a stated crimp diameter.

The hardened ring in a DIN 2353 / ISO 8434-1 fitting that bites into metric tube on the 24° cone. Pre-set it before final assembly, and do not reuse it on new tube.

A size in sixteenths of an inch: -8 is 8/16, or 1/2". On hose it is the nominal bore; on JIC and SAE fittings it is the tube outside diameter the fitting suits.

The segmented jaws a crimper closes around a ferrule. Each set covers a range of diameters; using the wrong one gives a crimp that measures right in one place and wrong in another.

The German standard for 24° cone bite-type tube fittings, now published as ISO 8434-1. Comes in LL (extra light), L (light) and S (heavy) series, named by tube outside diameter in millimetres.

On a hose elbow, the distance from the hose centreline to the sealing face of the connection. Short, medium and long drop elbows exist to clear neighbouring fittings.

A taper thread made so the crests and roots crush together and seal without sealant — NPTF is the common one.

A fitting that turns the line through an angle, usually 45° or 90°. Specify the angle, both ends and, for hose elbows, the drop length.

The European hydraulic hose standards: EN 853 for wire-braided hose (1SN, 2SN), EN 856 for spiral hose (4SP, 4SH, R12, R13), EN 857 for compact braid (1SC, 2SC).

A female end whose nut turns freely on the fitting body, so a hose can be connected without twisting it.

The outer shell of a hose fitting that is crimped down onto the hose. On a one-piece fitting it is permanently attached to the insert; on a two-piece fitting it is a separate part.

An SAE J514 compression fitting for inch tube that seals with a sleeve biting into the tube on a 24° seat, so the tube needs no flaring. Same thread as JIC.

A quick coupler whose two halves meet on flat faces, so almost no oil is lost and no air is drawn in on connection. The interchange is ISO 16028.

A port connection to SAE J518 / ISO 6162: a flange head with an O-ring, clamped to the port face by two half clamps and four bolts. Used from 1/2" upward where threads would be too large to tighten.

A length of hose with a fitting crimped or attached at each end, cut, built and tested as one part.

The nominal inside diameter of a hose, given as a dash size or in inches. For most hose the dash is the bore in sixteenths; SAE 100R5 and PTFE hose follow tube O.D. instead.

The fitting on the end of a hose: an insert for the hose bore, a ferrule over it, and a connection at the other end.

A fatigue test in which a hose assembly is pressurised and released hundreds of thousands of times at temperature, to SAE J343 or ISO 6803. It is what separates hose grades of the same burst pressure.

The stem of a hose fitting that goes inside the hose bore. Also called the nipple or tail.

An SAE J512 connection in which a double-flared tube end is held by a male nut on a 42° seat in the female body. Automotive brake and fuel lines.

The interchange standard for flat-face hydraulic quick couplers.

Metric straight-thread ports and stud ends that seal with an O-ring in a chamfer, like SAE ORB. The port carries a ring groove on its spot face to identify it.

The interchange standard for poppet and ball quick couplers. Series A is the European pattern, Series B the North American; the two do not connect to each other.

The international tube fitting standard: part 1 is the 24° cone (formerly DIN 2353), part 2 the 37° flare, part 3 ORFS.

The SAE J514 flare fitting: a UN/UNF straight thread and a 37° cone that seals metal to metal. The most common hydraulic fitting on American machines, and rated to about 5,000 psi in small sizes.

The Japanese flare fitting: a BSPP thread with a 30° seat. Looks like a BSP or JIC fitting and seals on neither.

A band of fine diamond or straight ridges rolled onto a part. On some ferrules it marks how far the crimp dies are set, which crimp charts give as "crimp to knurl".

A Japanese flare fitting with a metric parallel thread and a 30° seat, used on Komatsu machines. Not the same as the JIS 30° flare, which uses a BSP thread.

The printing along a hose cover: maker, grade, standard, size, working pressure and production date. Read it before ordering a replacement.

The nut that clamps a bulkhead fitting to a panel, or that holds an adjustable stud end in position against its backup washer.

The torque, or the flats or turns past finger tight, a connection is tightened to. Too little and it weeps, too much and the seat or thread is damaged.

An ISO 261 thread named by its real size: M18×1.5 measures 18 mm across the crests with 1.5 mm between them. Not every "metric fitting" has one — BSP and JIS fittings are often called metric too.

The lowest pressure at which a hose or fitting may burst in a qualification test. Working pressure is set from it by the safety factor.

The name of a size rather than a measurement. A 1/2" NPT thread measures 0.840" across; a -8 hose has a bore near, but not exactly, 1/2".

National Pipe Straight Mechanical: a straight pipe thread used on female swivels, sealing on a 30° seat. It mates a chamfered NPTF male.

National Pipe Taper (ASME B1.20.1) and its Dryseal version NPTF (B1.20.3). A 60° tapered thread that seals on the thread — NPT with sealant, NPTF by crushing its crests. Rated well below straight-thread ends at larger sizes.

The SAE J1926 straight-thread port: a UN/UNF thread with an O-ring on the male that seals in a chamfer at the port face. Same thread as JIC; different seal.

A crimp fitting whose ferrule is permanently attached to the insert, so no separate ferrule is ordered. Most modern hydraulic hose fittings are one-piece.

O-ring face seal, SAE J1453: an O-ring in a groove on the male face is squeezed against the flat female face. Rated to 6,000 psi in sizes to 1", and the usual cure for a joint that will not stop weeping.

The distance between thread crests: in millimetres for metric threads, or given as threads per inch for inch threads.

A set of toothed blades, each cut to one pitch. The blade that sits in the thread with no light under it gives the pitch.

The threaded or flanged opening in a pump, valve, cylinder or manifold that a fitting screws into.

The maximum working pressure a fitting or hose is recommended for. For a joint it is the lower of the two ends; for an assembly, the lowest of the hose and both fittings.

Holding a finished hose assembly at a pressure above its working pressure — typically twice it — to show the assembly holds before it ships.

A barbed fitting pushed into a matching push-lock hose with no clamp or crimp. For low-pressure air, water and oil only.

A two-half connector that joins and separates a line by hand, usually with valves that close as it parts. Named by its interchange: ISO 7241 A or B, ISO 16028 flat face, ISO 5675 agricultural.

A hose end assembled with spanners rather than a crimper — the socket screws onto the hose and the insert screws into it. Useful in the field; rated below a crimped fitting.

A tee with one end different from the other two. On a run tee the odd end is in line with one other; on a branch tee it is the side outlet.

The SAE J517 hose types, 100R1 to 100R19. The number names a construction, not a rank: R2 is two-wire braid, R12 four-spiral, R14 PTFE.

The SAE J512 flare fitting with a 45° seat, for low-pressure fuel, refrigerant and air lines. Not interchangeable with 37° JIC.

The ratio of minimum burst pressure to working pressure. Hydraulic hose and fittings are rated at 4:1.

Removing the cover (external skive) or inner tube (internal skive) from the end of a hose before fitting it, so the fitting grips the wire. Required by some fittings and forbidden by others.

Hose reinforced with four or six layers of steel wire laid in spirals rather than braided — SAE 100R12, R13, R15 and EN 856 4SP and 4SH. Used for high pressure and heavy impulse duty.

Screwing adapters into each other to get from one connection to another. Every extra joint is another leak path and another lever on the port.

A checklist for specifying hose: Size, Temperature, Application, Media, Pressure, Ends, Delivery. Missing any one is the usual cause of a wrong hose.

A thread whose diameter changes along its length, so it tightens and seals as it goes in. NPT and BSPT are taper threads; a straight edge along the male shows the taper.

Threads per inch: the pitch of an inch thread, counted along one inch of its length.

The outside diameter of rigid tube. Tube fittings are named by it, unlike pipe, which is named by a nominal size.

A hose installed twisted along its length. Even a few degrees shortens its life badly; the layline shows it as a spiral.

A crimp fitting in which the insert and the ferrule are separate parts, ordered and assembled together. Still common on larger sizes and older lines.

The Unified inch straight thread (ASME B1.1) used on JIC, ORB, ORFS and flareless fittings. Written as diameter and TPI: 9/16-18.

A slow seep of oil from a joint, not enough to drip quickly. Usually a damaged seat, a hard or missing O-ring, or a joint tightened wrong.

A cable or sleeve anchored either side of a hose fitting so that, if the fitting lets go under pressure, the hose cannot thrash.

Hose reinforcement of steel wire woven at an angle — one braid for SAE 100R1 and EN 853 1SN, two for 100R2 and 2SN.

The highest pressure a hose or fitting is rated to carry continuously, including surges. Also written MWP, maximum working pressure.