Union Rope’s Rated Capacity, Design Factors, and D/d Ratios Hand-tucked grommets and mechanically joined grommet Once this occurs, you’d have to perform frequent inspections and go through costly wire rope replacements.Įach sling type has different strength efficiencies, which is why we included a table below that describes the efficiency of various sling constructions with standard D/d Ratios: Mechanically spliced, single-part slings This can result in fatigue, irregular wear, and increased deterioration. Using a smaller D/d Ratio that’s not recommended for your lift can aggravate the bending motion. If you see a tight bending of the sling, this means there’s a smaller than recommended D/d Ratio. It can determine the sling’s efficiency or capacity reduction, and allow you to make corrections before continuing the lift. The D/d Ratio has a tremendous impact on sling capacity when using slings like wire rope, chain, polyester round slings, and nylon slings.

If the diameter is 10″ and the diameter of the rope is 1/2, the D/d Ratio is 20. This is 12″ divided by 3/8″ = 32, which 32 is the D/d Ratio. The diameter of the load divided by the diameter of the sling = D/d Ratio Photo Courtesy of Uniropeįor example, you’re picking up an object that’s 12 inches in diameter and you use a 3/8″ chain to pick it up. It is the ratio of the diameter (D) around the object which the sling might be bent, which could be a sheave or another object, then divided by the overall diameter (d) of the sling being used. The term D/d ratio works as a simple mathematical equation where you’re learning the diameter or distance of the load you’re picking up. To have a safe lifting operation, continue reading more about D/d Ratio, and the types of slings we carry at US Cargo Control to identify which is right for your lift. This could then lead to unsafe rigging practices. Identifying the D/d ratio when using any type of sling for a lift is critical, because if the lifting sling tightly bends over too much during the lift – the sling will get damaged. After all, it can be confusing as there are multiple factors you have to take under consideration such as knowing the weight of the load, the sling’s working load limit (WLL), and the load’s center of gravity.

You may wonder what D/d ratio is and what purpose it serves when lifting loads with different types of slings.

Crane rigging formulas