Rigging terms

Basket

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A basket is a sling passed around a structural member with both eyes brought down together, cradling the beam. Baskets around building steel (with protection) are how points begin.

Steel (wire rope sling)

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Riggers call wire rope slings "steel": fixed-length legs with swaged eyes used for baskets and bridle legs. Called by length ("give me a five-footer"), tagged, and inspected like everything overhead.

STAC chain (deck chain)

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STAC chain is high-strength alloy chain used in short lengths to fine-adjust bridle leg lengths, link by link. It is rated rigging chain, not hardware-store chain, and the distinction is load-bearing.

Trim

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Trim is the set height of a flown element ("trim the truss at 28 feet"). Trim height drives sightlines, focus, and load geometry; "at trim" means the rig is at show position.

Motor point vs house point

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The house point is the structural attachment; the motor point is the hoist hanging from it. Plots count both: what the building offers, and what the show hangs from each.

Bridle leg

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Each inclined member of a bridle, built from steels plus adjustable chain to a computed length. Leg tensions exceed their share of the load as the bridle flattens; the calculator does the math.

Apex

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The apex is the bottom junction of a bridle where the legs meet and the point loads. Placing the apex at the plot coordinate is the purpose of the whole assembly.

WLL vs breaking strength

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Working load limit is the maximum load hardware may see in service; breaking strength is where it fails. The ratio between them is the design factor, and rigging lives on WLL, never on breaking strength.

Design factor

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The design factor is the margin between rated working load and minimum breaking strength (commonly 5:1 or greater for slings). It absorbs the unknowns; it is not spare capacity to spend.

Shock load

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A shock load is a suddenly applied force (a snagged truss releasing, a dropped pick catching) that multiplies the static load several times over. Rigging practice exists largely to make shock loads impossible.

Dynamic load

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Dynamic loads arise from movement: accelerating hoists, automation effects, swinging scenery. Moving rigs are engineered to dynamic figures, not static weights, which is why automation carries its own standards.

Secondary (safety)

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A secondary is an independent backup suspension (safety cable or chain) that catches the load if the primary fails. Requirements vary by jurisdiction and hoist classification; when in doubt, one goes on.

E-stop

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The emergency stop kills motion in a hoist or automation system instantly from clearly marked controls. E-stop discipline (who can hit it, everyone; who resets it, one person) is part of every motor call briefing.

Load path

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The load path is the complete chain of elements carrying a load to the structure: fixture, clamp, truss, sling, shackle, motor, point, steel. Every element in the path is rated, or the path is not.

D8 / D8+ / C1

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European hoist classifications (from German BGV/DGUV practice) governing use over people: D8 hoists hold loads only with secondaries, D8+ may hold without moving over people, C1 systems may move loads over people. Which applies is a per-show engineering question.

Part of the eventools.io Show Dictionary, a free glossary of live event production terminology.