Nuts!

The nut above may be tight, but it does not fully engage the threads on the bolt. Good practice is to always leave at least 1/2 to 1 full bolt diameter protruding from the nut. Like this:

Washers need attention, too! A washer is a device to distribute the load from the nut evenly across the bolted surface. If the surface is flat and the backing hole is just barely larger than the bolt coming through it, then a non-hardened washer may do, but if it is subject to bending or is suspending a load overhead, then the washer should be graded the same as the bolt and nut (i.e. SAE Grade 5, or 8, or ASTM 305, as determined by the engineer certifying the system).

Walking the dog

Fortunately, common sense and better engineering criteria have become more prevalent in stage rigging, however, I still find many brand-spankin'-new facilities with equipment suspended on dog chain.

Some of the stuff I see is really scary. This batten at the left is just a smidgen from falling out of the rigging. Fortunately some one put a (pot-metal) screw through the bent wire chain so it would (hopefully) stay-put.














Here we see a dog-chain wrapped around an old loft block rope sheave. It too, secured with a pot-metal bolt.


This is a good example of multiple failure points all in series:
Bolted joint (at least this one was an SAE Grade 5 Bolt).
Open ended hook (if the batten snags on something and the line goes slack, then this can disengage).
Pot-metal Turn-Buckle with closed eye at bottom, but not a one-piece forged eye (it could bend open under load).
Bent wire S-Hook connected to track (no load rating for this either).
"Dog chain" is nothing more than a piece of bent solid wire. It is not load-rated for overhead lifting or suspension of loads over peoples' heads. Only Grade 63 or Grade 8 alloy steel chain is rated for that purpose. The next time you see bent metal parts holding up your rigging, or find open eye hooks, or non-graded bolts, or pot-metal turn-buckles, you might think about getting that fixed ASAP.