Sub assemblies are used for chain slings (or even wire rope slings) with three or more legs. There is not enough room to properly install four legs on a traditional master link, so a sub assembly is designed to fit two legs on each lower link and allow for the crane hook to connect to the largest top link. These Grade 100 sub assemblies are slightly oversized allowing them to fit over large crane hooks in the field. The bottom rings have an engineered flat to help prevent mismatching of incorrect chain component sizes. Proof-tested and certified with a 5:1 safety factor.