Wire rope is named for how it's built. "6x19 IWRC" means 6 strands, about 19 wires per strand, wrapped around an independent wire rope core. Those numbers tell you how the rope will wear, bend and carry load. This guide explains how to read a wire rope designation, the real difference between 6x19 and 6x37, IWRC vs fiber core, and a breaking strength chart by diameter.
Quick answer: 6x19 has fewer, larger wires, so it resists abrasion and crushing better. 6x37 has more, smaller wires, so it's more flexible and handles bending over sheaves and drums better. IWRC (a steel core) is stronger and resists crushing; fiber core (FC) is more flexible but weaker and can't take heat. For most lifting slings and crane work, 6x19 or 6x37 class with IWRC is the default.
How to read a wire rope designation
A typical callout looks like this: 1/2" 6x19 IWRC EIPS RRL Bright.
| Part | Example | What it means |
|---|---|---|
| Diameter | 1/2" | Nominal rope diameter, measured across the widest points of the strands |
| Strands | 6 | Number of outer strands laid around the core |
| Wires per strand | 19 | The class: approximate number of wires in each strand |
| Core | IWRC | Independent wire rope core (steel). FC means fiber core |
| Grade | EIPS | Steel strength: IPS (improved plow steel), EIPS (extra improved), EEIPS (extra extra improved) |
| Lay | RRL | Right regular lay, the standard. Lang lay and left lay are used for special jobs |
| Finish | Bright | Uncoated steel. Galvanized ropes are zinc coated for corrosion |
6x19 vs 6x37: what the class really means
"6x19" and "6x37" are classes, not exact wire counts. Each class covers several constructions with similar strength and handling.
| 6x19 class | 6x37 class | |
|---|---|---|
| Wires per strand | 15 to 26, no more than 12 on the outside | 27 to 49, with 15 to 18 on the outside |
| Common constructions | 6x19 Seale, 6x21 Filler Wire, 6x25 Filler Wire, 6x26 Warrington Seale | 6x31 Warrington Seale, 6x36 Warrington Seale, 6x41 Warrington Seale, 6x49 Filler Wire Seale |
| Outer wires | Larger | Smaller |
| Abrasion and crushing resistance | Better | Lower |
| Flexibility and bending fatigue life | Lower | Better |
| Sheaves and drums | Needs larger sheaves | Runs on smaller sheaves |
| Typical uses | Slings, haulage, dragging, winch lines where the rope rubs | Larger-diameter slings, crane hoists, ropes that bend often over sheaves |
The trade-off is simple: big outer wires wear slowly but break from bending sooner; small wires bend easily but wear through faster. At the same diameter and grade, both classes carry about the same nominal breaking strength.
IWRC vs fiber core
The core supports the strands and keeps the rope round under load.
- IWRC (independent wire rope core): a small wire rope of its own at the center. It adds strength (roughly 7 to 10% over the same rope with a fiber core), resists crushing on drums and sheaves, and stretches less. It's the standard for slings, cranes and hoists.
- Fiber core (FC): polypropylene or natural fiber. More flexible and a little lighter, but weaker, crushes more easily on multi-layer drums, and shouldn't be used above about 180°F because the core can be damaged by heat.
Choose IWRC for any lifting where the rope sees heavy loads, crushing or heat. Fiber core makes sense for light-duty, flexible applications where strength isn't the limit.
Wire rope breaking strength chart (6x19 and 6x37 class, EIPS IWRC)
Nominal minimum breaking strength for bright (uncoated) EIPS IWRC rope. 6x19 and 6x37 class ropes share these values at the same diameter. This is the breaking strength, not the working load: divide by the design factor (typically 5:1 for slings and running rope) before you lift.
| Diameter (in) | Breaking strength (tons) | Breaking strength (lbs) | Approx. WLL at 5:1 (lbs) |
|---|---|---|---|
| 1/4 | 3.40 | 6,800 | 1,360 |
| 5/16 | 5.27 | 10,540 | 2,100 |
| 3/8 | 7.55 | 15,100 | 3,020 |
| 7/16 | 10.2 | 20,400 | 4,080 |
| 1/2 | 13.3 | 26,600 | 5,320 |
| 9/16 | 16.8 | 33,600 | 6,720 |
| 5/8 | 20.6 | 41,200 | 8,240 |
| 3/4 | 29.4 | 58,800 | 11,760 |
| 7/8 | 39.8 | 79,600 | 15,920 |
| 1 | 51.7 | 103,400 | 20,680 |
| 1-1/8 | 65.0 | 130,000 | 26,000 |
| 1-1/4 | 79.9 | 159,800 | 31,960 |
| 1-3/8 | 96.0 | 192,000 | 38,400 |
| 1-1/2 | 114 | 228,000 | 45,600 |
Tons are 2,000-lb tons. Galvanized rope in the IPS and EIPS grades runs about 10% lower; EEIPS runs about 10% higher. A finished sling's rated capacity also depends on the end fittings and the hitch, so use the sling tag, not this chart, for rigging. See our wire rope sling capacity guide for sling ratings by hitch.
Choosing the right construction
| If the rope will… | Lean toward |
|---|---|
| Drag on the ground, rub structure or see abrasion | 6x19 class, IWRC |
| Bend repeatedly over sheaves or wind on a drum | 6x37 class, IWRC |
| Spool in several layers on a drum | IWRC (fiber cores crush) |
| Work near heat (furnaces, hot loads) | IWRC; never fiber core |
| Live outdoors, in mines or near water | Galvanized, or bright rope kept lubricated |
| Lift a single-part load that can spin | Rotation-resistant crane rope, not 6-strand |
| Make up a lifting sling | 6x19 or 6x37 class EIPS IWRC (6x37 at larger diameters) |
For cranes, high-performance 8-strand and compacted ropes often outlast standard 6-strand rope. Elko stocks Casar and Verope crane ropes, including rotation-resistant options like Verotop and Casar Starlift Plus.
Wear patterns by construction
- 6x19: resists abrasion, but its larger wires break sooner from bending fatigue. Watch for broken wires on the crowns of the strands where the rope runs over sheaves.
- 6x37: holds up to bending, but its small outer wires wear flat faster. Watch for worn, shiny flats and reduced diameter.
- IWRC: overloads and small sheaves can crush the core. Watch for flattening, strand gaps and core protrusion.
- Fiber core: the core can dry out, rot or absorb water, letting the rope lose diameter and shape. Watch for a sudden drop in diameter and strand looseness.
Remove rope from service for broken wire counts over the limit, reduced diameter, kinks, birdcaging, crushing, heat damage or heavy corrosion. Our guide to common wire rope sling failures shows what each looks like, and the rigging equipment checklist covers pre-lift inspection.
Get the right rope or sling
Elko Wire Rope builds custom wire rope slings (single, 2-leg, 3-leg and 4-leg) and stocks crane rope at our Salt Lake City, Elko, Phoenix and Safford branches. Tell us the load, the equipment and how the rope runs, and we'll spec the construction.
Wire Rope Construction FAQs
What does IWRC stand for in wire rope?
Independent wire rope core: a separate small wire rope at the center of the rope. It's stronger and more crush-resistant than a fiber core.
What does it mean when a wire rope is designated 6x19?
The rope has 6 strands with about 19 wires each. It's a class covering constructions from 15 to 26 wires per strand, such as 6x19 Seale and 6x26 Warrington Seale.
Is 6x37 stronger than 6x19?
No. At the same diameter, grade and core they have about the same breaking strength. 6x37 is more flexible; 6x19 resists abrasion better.
Is IWRC stronger than fiber core?
Yes, roughly 7 to 10% stronger at the same size and grade, and much more resistant to crushing and heat.
What does 6x19 FC wire rope mean?
A 6x19 class rope with a fiber core instead of a steel core. It's more flexible but weaker and not suitable for high heat or heavy crushing.
What is EIPS wire rope?
Extra improved plow steel, the most common grade for slings and general lifting. It's about 15% stronger than IPS.
