According to ASME B30.9, what is the minimum design factor for Synthetic Web, Synthetic Rope, Synthetic Round, Metal Mesh, and Wire Rope slings?

• A. 3
• B. 4
• C. 5
• D. 6

Answer: (C)

The key idea is safety margin. In ASME B30.9, the minimum design factor is the ratio of a sling’s breaking strength to its rated load (the working load limit you use in lifting). For the slings listed—synthetic web, synthetic rope, synthetic round, metal mesh, and wire rope—the standard requires this design factor to be five. That means the sling’s breaking strength must be at least five times its rated capacity. This margin helps cover real-world conditions that can increase loads, such as dynamic forces from lifting, angle effects, potential abrasion, wear, and misalignment, so the sling won’t fail under less-than-perfect conditions. Practically, if a sling is rated to lift a certain load, its actual breaking strength is five times that load, providing a robust safety cushion.