This is a large end 3/8" x 4" S-hook. 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 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.
This product should last 2 years in harsh conditions and up to 5 years in optimal conditions. Some conditions may require replacement sooner. Tensile strength is 1177 lbs.