Everything Breaks...The only question is under what load and under what conditions.
Ken DeLoria · June 23, 2017
Whether it’s a shackle, a hoist, a crane, or a beefy fly frame, never forget that everything breaks. The only question is under what load and under what conditions.
To address this issue, the rigging industry has adopted the term “SWL,” which stands for Safe Working Load. You might also see “WLL,” which stands for Working Load Limit. When you purchase a shackle, a pairing ring, or a length of wire rope, they’ll all carry a load rating – unless they are cheap copies of the real thing (more on this later).
Let’s start with the common anchor shackle. An anchor shackle is the bread and butter of the entertainment rigging industry.
It can be obtained in many sizes, and made from several types of material. It’s close cousin is the chain shackle, which normally carries the same ratings for a given size, but is not as commonly used (Figure 1 - slide 1).
The stated size of a shackle relates to the nominal diameter of the threads that secure the pin into the body of the shackle. The unthreaded section of the pin will always be larger in diameter.
This is important to know if you’re building a steel frame or fixture that the shackle will attach to. A 1/2-inch shackle will need a hole diameter of at least 5/8 of an inch or larger, to fit without jamming.
Loudspeaker rigging mainly utilizes shackle sizes of 1/2-inch, 5/8-inch, and 3/4-inch It’s rare to encounter any that are larger, though smaller ones are sometimes seen for light loads.
Typically, a 1/2-inch shackle will be rated at two-and-a-half tons or 5,000 pounds. A 5/8-inch shackle is usually rated at three-and-one-quarter tons (6,500 pounds). The rating is usually displayed on the shackle like this: “3¼T.”
But what does this mean precisely? Can you load them up to their stated rating? Absolutely not!