Rigging Hardware, Slings, and Below-the-Hook Devices
Core concepts
Hardware is the weak-link chain: shackles, hooks, master links, swivels, turnbuckles, eye bolts, pad eyes, and below-the-hook devices (spreader beams, lifting beams, plate clamps, vacuum lifters). Each has a rated capacity (WLL) based on a defined configuration. Candidates must know: shackle pin vs. bow orientation, hook throat opening and latch requirements, the difference between a spreader beam (compression member, legs angled) and a lifting beam (bending member, legs vertical), and that eye bolts are rated for axial loading only unless specifically designed for angular pulls.
Traps in questions
- Side-loading a shackle or hook - capacity drops sharply; hooks are rated for vertical load at the saddle.
- Using a shoulder eye bolt at an angle: capacity derates (roughly 25% at 45°, more beyond) and the eye can bend.
- Confusing proof load (typically 2× WLL for many hardware items) with WLL - proof load is a test, not a working limit.
- Assuming a spreader beam increases capacity; it only changes the sling angle and manages compression.
Rule of thumb
Match hardware WLL to the calculated sling tension, not the load weight. A 10,000 lb load on a 30° bridle gives 10,000 lb per leg - hardware must be rated for that, not 5,000 lb.
Worked example
A 6,000 lb load lifted by a two-leg bridle at 45° from horizontal: T = 3,000/0.707 = 4,243 lb per leg. Select shackles and hooks with WLL ≥ 4,243 lb (commonly a 3/4-inch screw-pin shackle at 6,500 lb WLL), and confirm the hook latch is functional and the load is centered in the saddle.