If you have ever stood in a parts crib staring at a coiled hose with a smeared layline and tried to figure out what it actually is, you are not alone. Hydraulic hose identification is one of those tasks every fluid power engineer eventually has to do, usually under pressure (literal and figurative), and the SAE J517 standard is the language you need to speak.
This guide walks through how to read a hose by its layline, decode the SAE R-class designation, and pick the correct replacement without guessing. If you want to skip the math, our Thread Identifier and Hose Selector calculators do the lookup for you.
What the Layline Tells You
Every compliant hydraulic hose carries a printed layline along its length. At minimum, you will find:
- Manufacturer name — Parker, Gates, Eaton, Continental, etc.
- SAE specification — e.g.
SAE 100R2AT - Dash size — the inside diameter in sixteenths of an inch (a
-08hose has a 1/2″ ID) - Working pressure — usually in psi or bar
- Date code or cure date — important for shelf life on rubber assemblies
If the layline is worn off, you fall back on construction inspection: count the reinforcement layers, identify wire vs. textile braid, and measure ID with calipers. The SAE R-class essentially encodes those construction details, which is why the standard exists in the first place.
The SAE J517 R-Class System
SAE J517 defines hose constructions R1 through R19. Each class specifies the reinforcement, minimum burst pressure, working pressure at each dash size, and temperature range. Here is what matters in the field:
R1 — One-Wire Braid
The workhorse for medium-pressure hydraulic lines. Synthetic rubber tube, single wire braid reinforcement, oil-resistant cover. Working pressures range from about 2,750 psi at -04 down to 350 psi at -32. Specify R1AT (the “AT” means “all temperature”) when you need -40°F to +212°F service.
R2 — Two-Wire Braid
The high-pressure cousin of R1. Two layers of wire braid double the working pressure. An R2-08 will handle ~5,000 psi vs. ~3,500 psi for R1-08. If you do not know what spec the old hose was and the equipment is industrial hydraulics, R2AT is the safe default replacement.
R3 — Two-Textile Braid
Lower pressure but very flexible. Used for return lines, suction service, and applications where tight bend radius matters more than burst rating.
R4 — Helical Wire Suction
A helically wound wire keeps the hose from collapsing under vacuum. This is your suction line spec — pump inlet, return tank lift, anywhere negative pressure is expected. Working pressures are low (300 psi max) but it will not pinch shut.
R5 — Truck Brake / Power Steering
One-wire braid with a textile outer braid (no rubber cover). Common in vehicle hydraulics and as air brake hose. The exposed textile braid is the visual giveaway.
R6 — Low-Pressure Return
One-textile braid, ~500 psi working pressure. Used for return-to-tank lines and lubrication circuits. Cheap and flexible.
R7 / R8 — Thermoplastic
Thermoplastic tube and cover, synthetic fiber reinforcement. R7 replaces R1 in many applications; R8 replaces R2. Cleaner, lighter, often used in paint plants and hydraulic test rigs because they do not shed rubber dust.
R9 through R15 — Four-Spiral and Six-Spiral
Heavy spiral wire reinforcement for impulse-rated hydraulic service. This is what you find on the boom and stick lines of an excavator. R12 and R13 are the most common; R15 hits 6,000 psi at larger dash sizes.
R16 / R17 — Compact Two-Wire
Same pressure as R1/R2 but with a smaller OD. Useful in retrofit jobs where the routing is tight and the original hose was bulkier.
R19 — High-Performance
The newest entry. Matches R2 pressure ratings with R16-style compact OD and improved bend radius. If you are speccing new equipment, R19 is often worth the small price bump.
Dash Sizes Without the Headache
Dash size is hose ID in sixteenths of an inch. So:
| Dash | ID (in) | ID (mm) |
|---|---|---|
| -04 | 1/4″ | 6.4 |
| -06 | 3/8″ | 9.5 |
| -08 | 1/2″ | 12.7 |
| -10 | 5/8″ | 15.9 |
| -12 | 3/4″ | 19.1 |
| -16 | 1″ | 25.4 |
| -20 | 1-1/4″ | 31.8 |
| -24 | 1-1/2″ | 38.1 |
| -32 | 2″ | 50.8 |
The fitting dash size does not always equal the hose dash size — a JIC -08 fitting has its own thread (3/4″-16) that mates to a -08 hose end. Mixing those up is the most common source of wrong-part orders.
Picking a Replacement
The decision tree is short:
- Read the layline. If readable, match SAE class, dash size, and fitting type. Done.
- If unreadable, identify by construction: count braids/spirals, check for textile cover, measure ID.
- Confirm working pressure at operating temperature — derate per the manufacturer’s chart if you are over 158°F continuous.
- Verify bend radius. Tight routing kills hose life faster than pressure does.
- Check fluid compatibility. Most R-class hose tubes are nitrile (NBR), which is fine for petroleum oils but not for phosphate ester or water-glycol fluids.
When the application calls for fire-resistant fluid or unusual chemicals, escalate to the manufacturer’s chemical compatibility chart before ordering. A wrong tube material will swell and fail in days.
Tools and Next Steps
Hydraulic system design is a chain of decisions and every one cascades. Once you have the hose figured out:
- Use the Pressure Drop Calculator to size the ID for acceptable line loss at your design flow rate.
- Use the Thread Identifier to confirm fitting compatibility before you cut anything.
- Use the Fitting Torque Calculator to get the assembly right — over-torque cracks the cone, under-torque leaks at the second pressure cycle.
If you work on hydraulics often, browse our full Fluid & Force category. We are building out the hydraulics suite with spec sheets for every R-class and dash combination, plus cross-reference tables for the four major hose manufacturers.
Got a hose ID question we did not cover? Send a photo of the layline and we will tell you exactly what it is.