I ran right out and tried that on 2 chains - didn't work. The single inner jaw is 1/16 shorter than the double outer jaw. Both curve the same direction. My first thot is that it's for stretching something since both jaws curve the same way.
The inner single jaw is 1/4" thick. The double outer jaw is 1" wide (2 - 1/4" thick jaws)with about 3/8+" between them.