I knew that "Proof" was a term used with a sour mash product and a cargo hold down chain. Something to do with how strong it was. But what exactly? Having a working knowledge of Jack I started looking for chain information. I found a good chain reference page that may be useful to others. http://www.1st-chainsupply.com/binderreq.pdf Look under Reference and there it is ... There is more then enough to hold one "Down"