What is WLL and what is a design factor (safety factor)?

WLL stands for Working Load Limit. It is the maximum load that a piece of rigging equipment is rated to safely support under normal use conditions. Every rigging component (shackles, motors, spansets, steels, truss) carries a WLL stamped or documented by the manufacturer. It is dangerous to exceed the WLL of any rigging component.

The design factor (historically called the safety factor) is the ratio between a component's ultimate breaking strength and its WLL. For example, a shackle with a breaking strength of 30,000 lbs and a WLL of 6,000 lbs has a design factor of 5:1. This built-in safety margin accounts for dynamic loads, wear, environmental factors, and repetitive use. Entertainment rigging hardware typically requires a minimum design factor of 5:1 for overhead suspended loads, while bolts have a minimum of 8:1. The older term "SWL" (Safe Working Load) has been replaced by WLL in current industry standards to avoid implying a legal guarantee of safety.