What is the minimum design factor (rating factor) for wire rope slings?

• A. 4
• B. 5
• C. 3
• D. 6

Answer: (B)

The safety margin between a sling’s breaking strength and the load it is allowed to carry is called the design factor. For wire rope slings, standards specify a minimum design factor of five to one. This means the rope’s breaking strength must be at least five times its working load limit (WLL). The five-to-one margin accounts for dynamic loads, shock, wear, and other conditions that can reduce performance, helping prevent sudden failure during lifts. For example, a sling with a WLL of 10,000 pounds would need a breaking strength of at least 50,000 pounds. This five-to-one factor provides a practical, widely accepted safety buffer, whereas smaller factors would reduce safety margins.