That chain looks to be what is know as " Long Link " in the Pulp mill and sawmill industry. The standard these days is 3/4" dia x 5" or 1' dia x 6" long. It's typical use is for conveyors moving sawdust, bark or chips. They normally have a "flight" which consists of 2 pieces of flatbar 3/4' x 3' x 24" or so long welded into the links and spaced about 5' or so apart. Your chunk of chain looks to be a slightly smaller version of this type of chain and my guess is somebody rigged it up to use as a tow chin of some sort.