Wire Rope Construction: 6×19, 6×36, and 19×7 Explained

Understanding Wire Rope Nomenclature

Wire rope construction is described by two numbers: strands × wires per strand. A “6×19” rope has 6 strands, each containing approximately 19 wires, twisted around a central core. But this naming convention is simplified — actual wire counts within the “class” can vary. The 6×19 class includes constructions from 15 to 26 wires per strand.

Major Construction Classes

Class	Wires/Strand	Flexibility	Abrasion Resistance	Fatigue Resistance	Crush Resistance
6×7	3-14	Low	Excellent	Poor	Good
6×19	15-26	Medium	Good	Good	Good
6×36	27-49	High	Fair	Excellent	Fair
6×61	50+	Very High	Poor	Excellent	Poor
8×19	15-26 (8 strands)	Very High	Fair	Good	Fair
19×7	7 (19 strands)	High	Good	Good	Excellent

6×19 Class — The Workhorse

The 6×19 class is the most widely used wire rope construction in the world. Its balanced properties make it suitable for the broadest range of applications:

• Common sub-types: 6×19 Seale, 6×19 Warrington, 6×25 Filler Wire
• Seale construction: Large outer wires over small inner wires. Best abrasion resistance in the class. Ideal for cranes, derricks, and hoists where the rope contacts sheaves and drums frequently.
• Warrington construction: Alternating large and small wires in the outer layer. Better flexibility than Seale with good abrasion resistance. Popular for general hoisting.
• Filler Wire: Small filler wires between inner and outer wire layers. Maximum number of wires for the class, giving best fatigue resistance. Good for high-cycle applications.

Minimum D/d ratio: 34:1 recommended, 26:1 minimum (where D = drum/sheave diameter, d = rope diameter)

6×36 Class — The Flexibility Champion

More wires per strand means smaller individual wire diameter, which translates to greater flexibility. The 6×36 class bends more easily around smaller drums and sheaves.

• Primary advantage: Can operate on smaller drums and sheaves than 6×19 — minimum D/d ratio of 18:1
• Trade-off: Smaller wires wear faster from abrasion. Not recommended for applications with heavy sheave wear.
• Best for: Mobile cranes, tower cranes, and applications requiring small drum diameters

19×7 — Non-Rotating Rope

19×7 construction uses 19 strands of 7 wires each, with the outer layer of strands twisted opposite to the inner layer. This counter-rotation cancels the twisting tendency under load.

• Primary advantage: Minimal rotation under load — critical for single-line crane hoists where an unguided load would spin
• Construction: 12 outer strands (right lay) over 6 inner strands (left lay) over 1 center strand
• Limitation: Must not be used with swivel connections — allowing rotation destroys the internal balance
• Best for: Tower crane hoists, single-line overhead cranes, pile drivers

Compacted Strand Rope

A manufacturing process that compresses (swages) each strand into a denser cross-section before the rope is closed. Benefits include:

• 15-20% stronger than standard rope of the same diameter
• Smoother outer surface — less abrasion on sheaves and drums
• Better crush resistance — important for multi-layer drum winding
• Longer service life in most applications
• Higher cost (10-20% premium over standard construction)

Selection Guide

Application	Recommended Construction	Why
Overhead bridge crane	6×19 Seale IWRC	Good balance, abrasion resistance on drum
Mobile crane main hoist	6×36 WS IWRC	Flexibility for multi-layer spooling
Tower crane	19×7 or 34×7	Non-rotating for single-line hoists
Elevator	8×19 Seale FC	Flexibility, smooth ride, fiber core cushioning
Guy wire/standing rigging	6×7 or 1×7	Low stretch, high abrasion resistance
Winch (vehicle)	6×19 IWRC or synthetic	General purpose, available everywhere
Mining hoist	6×36 compacted IWRC	Maximum fatigue life, crush resistance

Common Mistakes to Avoid

Avoiding these common errors can prevent equipment failure, regulatory violations, and serious safety incidents in the field.

• Ignoring the Fleet Angle: The angle between the wire rope and the drum or sheave should not exceed 1.5 degrees for smooth drums or 2 degrees for grooved drums. Excessive fleet angles cause uneven spooling and accelerate wear, reducing service life by up to 50%.
• Using Undersized Sheaves: The sheave diameter should be at least 18-20 times the rope diameter. Undersized sheaves cause severe bending fatigue. A 1/2-inch rope requires sheaves of at least 9-10 inches in diameter.
• Failing to Lubricate Properly: Wire rope requires regular lubrication to prevent internal corrosion and reduce friction between wires. The lubricant must penetrate to the core. Use wire rope lubricants specifically designed for the application, not general-purpose grease.
• Improper Dead-End Termination: Using fewer than the required number of clips, or installing U-bolt clips with the saddle on the dead end, can reduce termination efficiency to as low as 40%. Follow the Crosby clip spacing chart for correct number and torque values.
• Ignoring Broken Wire Criteria: ASME B30.9 requires rope retirement when 6 randomly distributed broken wires are found in one rope lay, or 3 broken wires in one strand in one lay. Continuing past these thresholds risks catastrophic failure.