Intermediate Rigging (RI) key terms

The maximum load a sling, shackle, or other rigging component is rated to lift in a specified configuration. It is assigned by the manufacturer and must never be exceeded, even briefly.

The load at which a rigging component fails completely and separates. It is determined by testing and is always higher than the working load limit by the design factor.

The ratio of breaking strength to working load limit. It provides a safety margin that absorbs wear, dynamic forces, and minor errors in load estimation. Common values range from 4:1 to 5:1 for slings.

The point where the entire weight of an object is considered to act. The hook must hang directly above this point, or the load will tilt and shift when lifted.

The condition in which a suspended load hangs level with its weight shared predictably among the sling legs. Unbalanced loads overload individual legs and cause uncontrolled swinging or rotation.

The angle measured between a sling leg and the horizontal load surface. As this angle decreases, tension in each leg rises sharply, so a flatter sling carries far more force than a steep one.

The pulling force carried along the length of a sling leg. It increases as the sling angle becomes more horizontal, even when the total load weight stays the same.

A sudden increase in force caused by rapid lifting, jerking, or a load dropping onto a sling. It can multiply the effective load several times and exceed the working load limit without warning.

The additional force produced by motion such as swinging, hoisting acceleration, or stopping. It adds to the static weight and must be considered when choosing slings and planning a lift.

A flexible assembly of chain, wire rope, synthetic webbing, or rope used to connect a load to a lifting hook. Each type has its own rating, inspection, and handling rules.

A hitch in which a single sling leg runs straight from hook to load. It uses the full rated capacity of the sling and produces no angle-related tension increase.

A hitch formed by passing the sling around the load and through itself, so the sling tightens as it lifts. It reduces capacity, and the reduction is greater when the choke angle is sharp.

A hitch in which the sling passes under the load and both ends attach to the hook, cradling the load. Capacity depends on the angle between the legs and the shape of the load.

One individual branch of a multi-leg sling assembly running from the master link or hook to the load attachment point. Each leg carries only part of the total load.

An assembly of two or more sling legs joined at a common point and spread to separate attachment points on the load. It distributes weight and controls load orientation.

A flat or round sling woven from high-strength synthetic fibers. It is light and non-marring but vulnerable to cuts, abrasion, ultraviolet degradation, and chemical damage, so inspection is critical.

A sling made from strands of steel wire laid into rope, usually with thimbles and fittings at the ends. It resists abrasion and heat but must be checked for broken wires and kinks.

A sling made of alloy steel chain links with master links and hooks. It tolerates abrasion and sharp edges but must be inspected for stretch, wear, cracks, and bent or twisted links.

A documented visual and physical examination of a sling before each use and at required intervals. It looks for wear, cuts, broken wires, corrosion, and tag loss that affect capacity.

The specific damage conditions that require a sling or component to be taken out of service immediately. Examples include missing tags, broken wires, severe wear, and deep cuts.

The manufacturer's label attached to a sling showing its type, capacity, and configuration. A sling with a missing or illegible tag cannot be safely rated and must be removed from service.

A U-shaped metal fitting closed by a pin or bolt, used to connect slings to loads or hooks. The pin must be fully seated and the shackle must not be side-loaded.

A curved fitting that connects the hoist line to the sling assembly. It must have a working latch to prevent sling eyes from slipping off, and the load must sit in the bowl.

A large single link at the top of a multi-leg sling assembly that gathers all legs and connects to the hook. It must be rated for the combined load of all legs.

A grooved metal insert placed inside a sling eye to protect it from abrasion and to spread the load around the pin. Using an eye without a thimble reduces capacity.

A rigid beam used between the hook and the load to keep sling legs vertical and prevent inward crushing forces. It allows lifting wide or flexible loads without side compression.

The manufacturer's table or curve giving the maximum permitted load for a crane at each radius, boom length, and configuration. It is the controlling authority for every lift.

The horizontal distance from the crane's rotation center to the center of the suspended load. Capacity decreases as radius increases, so it must be measured, not estimated.

The extended length of the crane's boom from its pivot point to the tip. Longer booms reduce capacity at a given radius and affect the chart section that applies.

The load chart capacity remaining after deducting the weight of rigging, slings, spreader beams, and any other lifting attachments. The net figure is what may actually be lifted.

The total weight being lifted, including the load itself plus all rigging and attachments below the hook. It must be compared against the net capacity from the load chart.

A written document that describes the load, crane position, rigging, capacity calculations, hazards, and sequence of a lift. It is required for critical or complex lifts and reviewed with the crew.

A lift that is unusually heavy, over people or sensitive equipment, or otherwise high risk, and therefore needs a formal engineered plan and additional review. Definitions vary by site policy.

A retractable stabilizing leg that extends from the crane carrier to widen its support base. Outriggers must be fully extended and set on firm, properly rated mats or pads.

A qualified worker who directs the crane operator using standard hand, voice, or radio signals. Only one person should signal at a time unless an emergency stop is needed.

A defined set of arm and hand movements used to tell the operator to hoist, lower, stop, or travel. Both operator and signal person must use and understand the same agreed signals.

A signal that any worker may give at any time to halt crane motion immediately because of imminent danger. The operator must obey it without question, regardless of who gives it.

A rope attached to a load and handled from a safe distance to control rotation and swinging. It keeps workers from touching the load directly while it is suspended.

The area beneath and around a suspended load that no one may enter during a lift. It protects workers from falling loads and from being caught between the load and fixed objects.