Every hydraulic hose carries its size in a simple code. Here's how dash numbers work, why inside diameter matters, and how to read the layline before ordering a replacement.
Hydraulic hose size is almost always written as a dash number — -4, -6, -8 and so on. The number is the hose's inside diameter in sixteenths of an inch: a -4 hose is 4/16, or 1/4 inch ID; a -8 is 1/2 inch; a -16 is a full inch. The same convention covers tube and many fittings, so a parts counter asks for "a dash eight," not a fraction.
The measurement is the inside diameter. OD changes with the reinforcement, so two hoses with the same dash size can have different ODs — when in doubt, size from the inside.
Small lines — pilot circuits, gauge lines and case drains.
The everyday ag size — remotes, loader circuits, small cylinders.
Mid-size work: backhoe circuits, wet kits, attachment lines.
Bigger flows — main circuits and higher-volume pump lines.
Large supply and return lines on excavators and cranes.
-5, -10, -20, -24 and -32 exist too — same math, divide by sixteen for the ID in inches.
A hydraulic circuit is built to move a set flow of oil. Squeeze that flow through a smaller hose and the fluid speeds up — more friction, more turbulence, more pressure drop, all of it turning into heat. Heat is hard on oil and seals, and it quietly steals engine power.
Going bigger isn't a free upgrade: an oversized hose is heavier, stiffer and often won't route through the original clamps, and it still necks down to the same ports. As a rule, the right replacement is the size the machine came with.
The jump between sizes is bigger than it sounds, because flow area grows with the square of the diameter — stepping from a -4 to a -6 more than doubles the area. "Close enough" isn't a sizing strategy.
The layline is the printed stripe running the length of the hose — the closest thing a hose has to a spec sheet. Formats vary by manufacturer, but a legible layline typically shows:
The printed rating applies to that hose in that size — ratings vary by manufacturer and series, so the layline and manufacturer spec are always the authority. If a hose has already let go, our guide on what to do after a blown hose covers the safe first steps.
Between the inner tube and cover sits the reinforcement — the "wire" shorthand. In plain terms, more reinforcement generally means higher pressure tolerance, but the printed rating, not the wire count, is what you trust.
A single braided layer — lighter, more flexible, generally on lower-pressure and return lines.
Two braided layers — the workhorse construction on most mobile equipment.
Spiral-wrapped layers instead of a braid — stiffer, tougher, built for high-impulse circuits on excavators and big iron.
Within the same series, rated pressure typically drops as diameter goes up, so a small 2-wire may out-rate a large one. Never assume a rating from construction alone — check the layline or manufacturer chart and match what the machine calls for.
Size is half of a hose order — length is the other half, with two numbers in play. Cut length is the hose alone, before fittings go on. Overall length is the finished assembly, end to end, fittings included. Where exactly an angled fitting gets measured from varies between shops, so the safest reference is the old assembly itself:
Every machine is its own spec, so treat these as patterns, not rules — the layline always wins. Still, the same shapes repeat:
Farm equipment around Delano and Shafter tends to run mid-size braided hose — remotes and implement lines commonly land around -6 to -8, though big iron goes heavier.
Boom, stick and bucket circuits typically call for spiral hose in the larger sizes, with small pilot lines at the joysticks — one machine mixes several sizes.
The westside leases around Taft are hard on hoses — heat, sun and vibration wear the layline fast. Sizes vary widely by unit, so we identify at the machine.
Whatever the machine, we measure the old hose, match ID, rating, length and ends, and build the replacement on-site. See what we fix for the full list.
Call dispatch, tell us what let go and where the machine sits — we'll identify, build and crimp the right hose on-site.