This is a large end 5/16″ x 4″ S-hook.  These can be used with all of our chains.  Our commercial quality large end S-hooks are designed to fasten chain to swing hangers and swing seats to help prevent binding. They are plated to help resist rust. S-hooks that are not bought from a playground manufacturer do not have the quality control and have been known to break with the first “swinger”.  Tensile strength is 745 lbs.