Referring to the rigger reference booklet, what is the capacity of a 4 inch grade 100 alloy chain three-leg sling lifting at a 45 degree angle?

• A. 50,000 pounds
• B. 74,900 pounds
• C. 100,000 pounds
• D. 60,000 pounds

Answer: (B)

Understanding how a multi-leg sling shares load is key. When you have a three-leg chain sling at an angle, the weight being lifted is shared among the legs, but each leg must be able to carry more tension than simply W divided by the number of legs because the legs are not vertical. The vertical support from each leg is the leg tension times the cosine of the angle from vertical. So the total load the sling can safely lift is determined by the sum of those vertical components: W = number of legs × leg tension × cos(angle). The chain’s WLL sets the maximum allowable tension per leg, so the maximum safe load occurs when each leg is loaded to its WLL.

For a 4 inch Grade 100 chain, the WLL per leg from the reference table is about 35,300 pounds. With three legs and an angle of 45 degrees from vertical, cos(45°) is 0.707. Multiply: 3 × 35,300 × 0.707 ≈ 74,900 pounds. That’s why the capacity at this angle is around 74,900 pounds. If the angle changed, the cos factor would change the total accordingly, which is why the 45-degree value is specifically used here.