I thought it was supposed to be a cheap version of the anti-static straps you see on some cars.
Way way back in the 60s, anti-static suddenly became fashionable.
I reckon some hardware shop ordered the wrong length of bog chain, probably a units mix up.
ie, he wanted a 15 metre roll of bog chain, but got 15 miles instead.
He then had to find a way of shifting 15 miles of bog chain fairly quickly, and had a brain wave.
If I can convince folk that a length of bog chain bolted to their car will stop them getting static shocks, I’ll shift it in no time.
It worked, he did, going by the number of cars that suddenly grew a length of bog chain in the 60s 
Technology has moved on. Anti-static straps are now plastic, so a length or two of plastic chain will do the same job, right?