Wire Rope Types: Composition, Grades & How to Choose

A crane on an industrial site, a winch line on a barge, and a sling in a fabrication shop may all use Wire rope, but rarely the same variety. Differences in strand count, wire arrangement, center support material, lay direction, and steel grade all influence how a rope handles load, surface wear, bending, and environmental exposure. Many people refer to all of these products simply as "steel cable" without distinguishing assembly details. Choosing the wrong configuration can lead to accelerated wear, reduced service life, and rope that does not perform as expected under tension.

What Is Wire Rope?

Wire rope is a mechanical cable made of multiple metal wires twisted together to form strands, which are then laid helically around a central support. According to the Wire Rope Technical Board (WRTB), wire rope consists of three primary elements:

• Wires: The smallest individual elements, typically drawn from high-carbon steel or corrosion-resistant alloys.
• Strands: Groups of wires twisted together in a specific pattern, then laid around the center to form the finished rope.
• Core: The center support running the length of the rope, maintaining strand position under heavy tension. The material can be fiber or steel.

In the lifting industry, "wire rope" is the formal term used in OSHA regulations and ASME B30.9 (2021 edition). Wire rope slings are valued for their strength, durability, abrasion resistance, and ability to conform to the shape of loads.

Wire Rope Categories (Strand x Wire)

The arrangement of wires and strands determines the rope's flexibility, strength, and resistance to external wear. Wire rope classification uses a nominal designation: the first number indicates strand count, and the second indicates wires per strand.

6x19 Classification

The 6x19 class is the most widely used general-purpose variety, offering a balanced combination of flexibility and resistance to surface wear. While "19" is the nominal number, actual configurations may include 6x21 filler wire rope or 6x25 filler wire rope. It is robust enough to handle abrasive environments while remaining flexible enough for many pulley systems.

6x37 Classification

With more wires per strand than the 6x19 class, this category offers much greater flexibility. However, because the individual wires are finer, they have less resistance to surface abrasion. The 6x36 Warrington Seale is one of the most common configurations in this category, often used in cranes where the rope must navigate smaller sheaves.

6x7 Classification

This category features fewer, larger wires per strand. This results in a much stiffer rope with high resistance to surface wear. Because it does not bend easily, it is better suited for stationary applications like standing rigging, guy wires, and guard rails rather than active hoisting.

19x7 Classification (Rotation-Resistant)

This is a specialized rotation-resistant variety using two layers of strands laid in opposite directions. The inner layer is typically left lay, while the outer 12 strands are right lay. These opposing forces counteract the rope's natural tendency to spin under a load, making it essential for crane applications using single-part lines.

Understanding Lay Types

The "lay" of a wire rope describes the direction in which strands wrap around the center and the direction wires wrap within each strand. This affects how the rope interacts with drums and sheaves.

• Right Regular Lay (RRL) : The most common variety. Wires within each strand are laid in the opposite direction to the strands themselves. This makes the rope easy to handle and less likely to untwist or kink. RRL meets the requirements of most industrial equipment.
• Left Regular Lay (LRL) : Similar to RRL, but the strands wrap in the opposite direction (counter-clockwise). This is specified only when equipment design or specific reeving requirements demand it.
• Lang Lay : Here, the wires and strands are laid in the same direction. This creates more surface contact with sheave grooves and drum surfaces, which significantly improves bending fatigue life. However, Lang Lay is more prone to kinking and untwisting, so it should only be used in specific, controlled environments.

Internal Center Support (Core Types)

The center of the rope supports the strands and prevents the rope from collapsing under heavy pressure.

1. Fiber Core (FC) : Made from natural or synthetic fibers. These provide excellent flexibility and internal cushioning between strands. However, they offer less resistance to crushing and are more susceptible to damage from extreme heat or moisture.
2. Independent Wire Rope Core (IWRC) : A small, separate wire rope that serves as the center. IWRC provides significantly higher strength, better crush resistance, and greater heat tolerance. It is the standard choice for heavy-duty lifting and most sling applications.
3. Wire Strand Core (WSC) : A single strand of wire used as the center. This is less common in lifting but used in some specialized rigging.

Wire Rope Grades & Strength

The grade of wire rope refers to the tensile strength of the steel. Each higher grade is approximately 10% stronger than the one before it.

Material Selection

Carbon Steel (Bright and Galvanized)

Most industrial lifting rope is carbon steel. Bright (uncoated) wire rope offers the highest strength for its grade. Galvanized rope features a zinc coating for corrosion protection in outdoor or wet environments, though the coating process may slightly reduce breaking strength compared to a bright finish.

Stainless Steel

Stainless steel (typically Type 304 or Type 316) is selected for high-corrosion areas. Type 316 is particularly effective in marine settings with salt water and chlorides. While it excels in longevity, stainless steel generally has a lower breaking strength than carbon steel of the same diameter.

How to Choose the Right Rope

• Application : Slings often utilize 6x19 or 6x37 classes with IWRC. Active running ropes require the flexibility of 6x37, while stationary rigging may use 6x7.
• Flexibility vs. Surface Wear : More wires per strand increase flexibility but decrease resistance to abrasion.
• Environment : Use galvanized or Type 316 stainless steel for marine or chemical exposure; bright carbon steel is sufficient for dry, indoor use.
• Support : Choose IWRC for heavy loads and heat exposure; fiber core for tasks where flexibility is more critical than maximum capacity.

For high-performance lifting, Holloway assembles Wire Rope Slings, including three-part and nine-part EIPS configurations, to ASME B30.9 requirements, ensuring every sling is proof-tested.

Inspection and Removal Criteria

Wire rope requires regular evaluation by a qualified person. Conditions that indicate a rope should be removed from service include:

• Broken Wires : Visible breaks indicate fatigue and wear.
• Kinking : A permanent weak point caused by a loop being pulled through.
• Bird Caging : Permanent strand separation, often caused by sudden tension release.
• Crushing : Flattening of the rope from improper drum winding.
• Core Protrusion : The center supports pushing through the outer strands.
• Heat Damage : Discoloration from exposure to excessive temperatures.
• Missing Identification : Slings without legible tags cannot be confirmed for capacity and must be removed.

Explore more details about wire rope slings

• Blog : Wire Rope Sling Angles: What Every Rigger Should Know, Learn how hitch angles affect load capacity.
• Blog : How to Choose Wire Rope Slings: 7 Tips , A deeper dive into selecting the right sling for your shop.

Take the Next Step

Looking for wire rope slings built to the highest safety standards? Browse Holloway HoustonI's full line of three-part, nine-part, and eye-and-eye configurations, all proof-tested before shipment.

Need expert advice? Request a quote or call 713-675-3900 to speak with a rigging specialist today.