"AL" wrote in message news:%p59c.13948$JO3.22918@attbi_s04...
I believe, but am not 100% sure, that a chain rated for overhead lifting
has
a greater safety margin and is designed to fail somewhat gracefully. For
example, a regular chain rated for 1000 pounds may actually be designed
for
2000 pounds. A overhead lifting chain rated for 1000 pounds may be
designed
for 4000 pounds. And when overloaded, the hooks on the overhead chain are
designed to bend first (instead of a link breaking first), giving ample
warning instead of just letting the load drop. But again, I'm not 100%
sure
about this.

I keep a metallurgical souvenier, a short length of high-grade chain with a
couple of links that are stretched to about 2X their nominal length. The
one that eventually failed had been both stretched and bent around a sharp
90 degree corner (truck frame).

The chain was left over from the first attempt at pulling on a loaded 10
wheel truck sunk in mud up to its axles. Just a wild guess, it broke at
around 20,000 lbs force on a 3/8" chain.