Rigging Hardware and Slings
Hardware Fundamentals
Shackles, hooks, links, swivels, turnbuckles, and eyebolts all have rated capacities and specific loading directions. A screw-pin shackle must be fully seated with the pin tight; a bolt-type shackle needs the nut fully engaged and the cotter pin installed. Hooks must have a functioning latch and must not be loaded on the tip or the back. Eyebolts are rated for axial pull only - loading at an angle dramatically reduces capacity.
Sling Types and Their Limits
Wire rope slings resist abrasion but fail from broken wires, kinks, and bird-caging. Chain slings tolerate heat and sharp edges but fail from stretched links, cracks, and wear at the bearing points. Synthetic web slings are strong and soft but vulnerable to cuts, UV degradation, and chemical attack; they must not be used where they contact sharp edges without protection. Synthetic round slings must have their covers intact - a damaged cover means removal.
Sling Angle and Tension
As the angle from horizontal decreases, tension in each leg rises sharply. Two-leg slings at 60° from horizontal carry about 0.58 times the load per leg; at 30° that rises to 1.0 times the load per leg. Never exceed the manufacturer's minimum angle; typical practice prohibits sling angles below 30° from horizontal without engineering approval.
Common Traps
Questions test whether you know that a sling's capacity is reduced by the hitch type (choker and basket differ from vertical) and that a tag showing a vertical rating does not authorize a choker pick.
Worked Example
A 4,000 lb load on a two-leg bridle at 60° from horizontal: each leg tension = (load/2) / sin 60° = 2,000 / 0.866 ≈ 2,310 lb. Select slings rated at least that in the vertical configuration for that hitch.