In a theatrical stage rigging
system the spreader plates
are the thin pieces of metal that hold the counterweight
in place on the arbor
A typical arbor will have two spreader plates. One will rest above the lower few weights on the arbor. Ideally the weights below this spreader plate are equal to the weight of an empty batten. All counterweight above the spreader plate should be equal to the weight of any lighting equipment or flown scenery attached to the batten.
The second spreader plate is located above all of the counterweight and is secured to the arbor with two thumbscrews. Should the arbor come to a sudden stop the top spreader plate prevents any of the counterweight below it from being jarred off of the arbor.
The top spreader plate always poses a problem when loading or unloading weight on the arbor. Use a bulldog clip or some other quick clamp to hold the spreader plate up out of your way when loading or unloading.
It may seem strange, but when brought to a sudden stop, those 50 pound lead counterweights will bounce. For the safety of the rigger and everyone else on stage,
Always securely clamp the top spreader plate in place!
A 50 pound chunk of lead falling from 80 or 90 feet will kill you.
Part of the Stage Rigging Metanode