Advanced Rigging (RA) key terms

The single point where the entire weight of an object is considered to act; for a uniform object it sits at the geometric center, and for irregular loads it must be located by calculation or test lift.

The turning effect of a load, calculated by multiplying its weight by the horizontal distance from the pivot or tipping line to its center of gravity; used to check stability and crane capacity.

The force carried by each sling leg, found by dividing the share of load taken by that leg by the cosine of its angle from vertical; steeper legs carry less tension.

The angle measured between a sling leg and the horizontal load surface; as this angle decreases, tension in the leg rises sharply, so shallow angles are avoided.

A multiplier applied to load weight to estimate sling-leg tension for a given angle; for example, a 60-degree leg uses about 1.155 and a 45-degree leg uses about 1.414.

The maximum mass or force a rigging component is authorized to support in a specific service, established by the manufacturer and reduced by any applicable derating factors.

The ratio of a component's breaking strength to its working load limit; it provides a margin of safety against wear, dynamic forces, and unexpected loading conditions.

A test load applied to a component, usually greater than its working load limit but below yield, to verify strength and detect defects before the item is placed in service.

A U-shaped connector with a pin or bolt used to join slings to lifting eyes, hooks, or other hardware; it must be loaded along its axis and never side-loaded.

A large forged ring or link at the top of a multi-leg sling assembly that gathers the legs and provides a single attachment point for the crane hook.

One branch of a multi-leg sling assembly running from the master link or hook down to the load connection; its tension depends on share of load and angle.

A below-the-hook device that holds sling legs apart at a fixed distance so they stay more vertical, reducing horizontal compression on the load and lowering leg tension.

A below-the-hook device designed to carry bending and shear loads between attachment points, typically rated for a stated capacity and often used to clear obstructions above the load.

Any lifting attachment that connects the crane hook to the load, such as a spreader beam, lifting beam, clamp, or vacuum lifter, and that requires its own rated capacity.

A manufacturer-supplied table or graph giving the maximum allowable load for a crane at specified radii, boom lengths, and configurations; it governs every lift.

The maximum load a crane or hoist may handle under stated conditions, as published by the manufacturer after deductions for attachments and configuration-specific limits.

A defined set of arm and hand movements used to direct crane operators when voice or radio contact is unreliable; only one designated signalperson should transmit them.

A person who has been trained and evaluated as competent to direct crane movements using standard signals, and who understands crane dynamics, rigging, and emergency stop procedures.

A rope attached to a load to control rotation and sway from a safe distance, keeping riggers clear of the load path while the crane moves the load.

The route a load travels during a lift and the zone beneath and around it; keeping personnel outside this area is the primary defense against struck-by injuries.

The pattern in which strands are twisted around the core, described as regular or lang, and in a direction such as right or left; lay affects handling, abrasion resistance, and rotation.

A group of wires helically twisted together to form one of the outer members of a wire rope; strand count and wire arrangement determine flexibility and strength.

A wire rope built with opposing lays or special strand designs that resist twisting under load, reducing load spin and the risk of kinking during single-line lifts.

A lifting sling made from high-strength synthetic fibers such as nylon or polyester, available as web, round, or rope types, and sensitive to cuts, heat, and chemical attack.

Padding, softeners, or edge guards placed between a sling and sharp or abrasive load surfaces to prevent cutting, abrasion, and strength loss during a lift.

A self-propelled or track-mounted lifting system using hydraulic rams and a controlled header beam to raise and travel heavy loads at low height in constrained spaces.

A temporary vertical support structure of stacked cribbing or steel sections used with hydraulic jacks to raise a load in controlled increments while blocking is inserted.

Layered timber or manufactured blocks placed under a raised load to hold it at height; cribbing must be stable, level, and sized for the load it supports.

Moving a load horizontally across a surface on rollers, skid shoes, or a lubricated track, using controlled pushing or pulling rather than lifting.

A system of steel rollers or tank rollers placed under a load to reduce friction during horizontal movement; rollers must be sized, aligned, and monitored for crushing hazards.

A lift that exceeds routine criteria, such as high value, unusual configuration, multiple cranes, or personnel beneath the load, and therefore requires a written engineered plan and added review.

A documented description of a lift covering load weight and center of gravity, rigging arrangement, crane capacity, personnel roles, hazard controls, and contingency steps.

A sudden application or release of force that produces dynamic stresses far above static load, often caused by jerking, snatching, or rapid load release.

Published limits that define when a sling, rope, or hardware item must be taken out of use, such as broken wires, cuts, excessive wear, or deformation.

A scheduled examination of rigging and lifting equipment performed at defined intervals by a designated person, with results recorded and defective items tagged out.

A person capable of identifying existing and predictable hazards and who has authority to take prompt corrective action to eliminate them, as defined by safety regulations.

A marked area around a lift or crane operation where unauthorized personnel are prohibited, established to protect workers from falling loads, swing, and pinch points.

A dangerous condition in which the load block is drawn up against the boom tip, causing rope damage and potential failure; limit switches and operator awareness prevent it.