Wire rope looks like a thick metal cable, but it's really a hierarchy: wires twist into strands, and strands twist around a core. That layered helical construction is what lets a steel cable bend around a sheave without the surface fibers snapping — every wire shares the strain instead of one outer fiber taking it all.

The naming code. A rope like 6×19 IWRC means 6 strands, 19 wires per strand, wrapped around an Independent Wire Rope Core. More wires per strand = more flexibility but less abrasion resistance. Fewer, thicker wires = tougher outer surface but stiffer rope. The classic tradeoff:

• 6×7 — few, large wires. Stiff, abrasion-resistant. Used for standing rigging, guy wires.
• 6×19 — the general-purpose default. Cranes, hoists, winches.
• 6×37 — many fine wires. Very flexible, bends around small sheaves. Used on mobile cranes with tight reeving.

Core choice matters. A fiber core (FC) cushions the strands and holds lubricant — good for lighter loads and shock. An independent wire rope core (IWRC) adds ~7-10% strength and crush resistance, and it doesn't collapse under heat. Overhead cranes almost always use IWRC.

Lay direction. In regular lay, wires within a strand twist opposite to the strands themselves — the wire surfaces appear parallel to the rope axis. It resists spinning under load and is the default. In Lang's lay, wires and strands twist the same direction. Longer wire contact means better fatigue and abrasion life, but the rope wants to unspin — you must fix both ends.

Sheave sizing rule of thumb. The D/d ratio (sheave diameter to rope diameter) governs fatigue life. For crane service, minimum D/d ≥ 18; for long life, aim for 30–40. Halving D/d can cut rope life by 5×. That's why crane hook blocks are big — not for strength, but to let the rope survive bending cycles.

Quick calculation. A 1/2" 6×19 IWRC rope has a minimum breaking strength around 23,000 lb. With a standard design factor of 5 for general hoisting (10 for personnel), the safe working load is ~4,600 lb. Never derive capacity from wire diameter alone — the construction changes it by 20–30%.

Retirement criteria. Replace when 6 or more randomly-distributed broken wires appear in one lay length, or 3 in one strand. Also retire for corrosion, kinks, heat damage, or diameter reduction >5%.