Rigging Hardware: Shackles, Hooks, Eyebolts, and Spreader Bars

Rigging Hardware: Shackles, Hooks, Eyebolts, and Spreader Bars

Rigging hardware connects the load to the hoist or crane. Every component in the rigging system must be rated for the forces it will carry, properly assembled, and inspected before each lift. A single undersized or damaged piece of hardware can cause a dropped load, which injures workers and destroys property. Understanding how to read, select, and assemble rigging hardware is a core competency for any rigger.

Working Load Limit and Safety Factor

Every piece of rated rigging hardware carries a Working Load Limit (WLL) stamped or embossed directly on the body. The WLL is the maximum load the manufacturer allows in normal service. Rigging hardware is manufactured with a design factor (often called a safety factor) built in — commonly 4:1 or 5:1 — meaning the hardware is proof-tested to several times its WLL before it leaves the factory. You never work up to or beyond the WLL; it is the ceiling, not a target. Never use hardware that has no legible WLL marking.

Shackles

Shackles are the most common rigging connector. The two main types are:

• Screw-pin shackles: The pin threads into the bow. Fast to rig but can unscrew under rotation or vibration. After threading the pin fully home, mouse the pin with seizing wire through the hole in the pin and around the shackle bow so it cannot back out.
• Bolt-type (safety) shackles: Use a bolt, nut, and cotter pin. The cotter pin locks the nut and prevents the bolt from turning. Preferred when the pin may be subjected to rotation or where a shackle must remain in service for extended periods.

Shackle orientation matters. The load must bear on the bow (the curved section), not on the pin. When two sling legs are attached, both go on the bow; the single load point connects through the pin end — or a single sling leg may be on the pin as long as the primary tension rides on the bow. Never side-load a shackle unless the WLL has been specifically de-rated for that angle per the manufacturer's data.

Inspection points: Look for cracks, gouges, elongation of the bow, corrosion pitting, and a pin that does not thread smoothly. Remove any shackle from service that shows these defects.

Hooks

Crane and rigging hooks are forged steel, and all must have a safety latch that keeps slings or shackle bows from accidentally slipping out. The load must seat in the saddle (the deepest part of the throat), not on the tip — tip-loading can straighten the hook. Never force the latch open by hammering.

Swivel hooks allow the load to rotate without twisting the sling. They are used on the master link end of a sling assembly. The swivel bearing must spin freely; a frozen swivel defeats its purpose. Check the latch, the hook body for cracks or bending, and the swivel for wear or corrosion.

Eyebolts

Forged eyebolts thread into tapped holes in equipment to provide a lift point. Two critical rules:

1. Use only forged eyebolts, never cast. Cast eyebolts are not rated for lifting.

2. Shoulder (shouldered) eyebolts are required for any angled pull. A plain (shank-only) eyebolt loaded at an angle loses rated capacity rapidly and can fail without warning. Shoulder eyebolts handle angular loads when de-rated per the manufacturer's chart.

Torque the eyebolt fully and ensure the shoulder seats flat against the surface. The eye must be aligned in the plane of the sling pull. Inspect for cracks at the shank-to-eye transition and thread condition.

Spreader Bars

A spreader bar is a rigid compression member that holds sling legs apart so they pull more vertically on attachment points. This reduces horizontal compressive forces on the load (important for fragile or top-heavy loads) and lowers the sling angle effect. Spreader bars are rated for their specific configuration; never exceed the rated capacity. Ensure the end fittings (usually shackles or hooks) are secured and that the bar itself shows no bends, cracks, or damaged end fittings. Keep personnel out from under any suspended spreader bar assembly.

Sling Angle and Hardware Loading

As sling legs angle outward from vertical, tension in each leg increases. At a 60-degree angle from horizontal (a common benchmark), each leg carries more load than at a 90-degree (straight vertical) pull. This increased tension applies equally to every shackle, hook, and eyebolt in the system. Always account for sling angle when selecting hardware rated capacity.

Assembly Best Practices

1. Lay out all hardware and confirm WLL markings before rigging.

2. Thread screw-pin shackle pins fully home (hand-tight, then a partial turn with a tool) and mouse them.

3. Install bolt-type shackle cotter pins so both legs are bent open.

4. Orient shackle bows to carry the load; align hook throats with the load direction.

5. Ensure safety latches are fully closed.

6. Conduct a trial lift — raise the load only a few inches, pause, and inspect the entire assembly before continuing.

Safety Reminders

• Never stand under a suspended load.
• Wear leather gloves when handling hardware and wire.
• If any component's WLL is unknown or illegible, remove it from the rigging bin and tag it out of service.
• OSHA standards for rigging hardware require proof-testing documentation and visible WLL markings. Hardware without markings must not be used for lifting.