What is rigging hardware and what are working load limits?

Rigging hardware is the collection of metal components that connect wire rope slings, chain slings, or synthetic slings to the crane hook and to the load's attachment points. These components are load-bearing elements in the rigging system, and a failure of any single piece of hardware drops the load. Each component must be selected, inspected, and used within its Working Load Limit for the specific application and connection geometry being used.

Common Rigging Hardware Components

Shackles are the most commonly used rigging hardware. They connect sling eyes to master links, spreader bars, and load attachment points. Shackles come in two primary styles: screw pin shackles and bolt-type (round pin) shackles. Screw pin shackles are used for temporary connections that will be assembled and disassembled regularly. Bolt-type shackles are used for permanent or long-term rigging assemblies. Each shackle has its WLL stamped on the bow. Hooks with safety latches are used to connect the rigging to the crane's load block or to the load itself. The safety latch must be functional before use; a hook with a missing or bent latch must be removed from service.

Swivels allow the rigging to rotate without transmitting torque to the slings, which is important when handling loads that may rotate during the lift. Master links, also called pear links or oblong links, are used to gather multiple sling legs into a single connection point at the hook. Each has a rated WLL that applies to the full multi-leg loading, not per-leg. Turnbuckles allow length adjustment in the rigging assembly and must be rated for the tensile load they will carry, not just the assembly weight.

Working Load Limit vs. Breaking Strength

The WLL is the maximum load that a rigging component may carry under normal working conditions. The WLL is not the breaking strength of the component. The relationship between WLL and breaking strength is the design factor, which for most standard rigging hardware under ASME B30.26 is 4:1 or 5:1. This means a shackle with a 4,750-lb WLL has a minimum breaking strength of approximately 19,000 lb to 23,750 lb. The design factor exists to provide a margin for dynamic loading, shock loading, and the natural variation in material properties. Rigging must never be loaded to or near the breaking strength; the WLL is the operational limit.

Inspection Requirements

ASME B30.26 and OSHA 1926.251 require rigging hardware to be inspected before each use. The inspection covers: visible deformation, cracks, or gouges; corrosion, pitting, or surface degradation; stretch or elongation beyond the manufacturer's removal criteria; proper seating of pins and nuts; and legibility of the WLL marking. Hardware with any deficiency must be removed from service immediately. Hardware that cannot be positively identified by WLL marking must also be removed from service, because an unmarked shackle of unknown rating cannot be safely assigned a load limit for planning purposes.