These EPDM swing seats have been tested and approved for safety up to 1040 lbs. EPDM: Ethylene-propylene-diene-monomer which is a synthetic rubber material which helps prevent crazing, cracking and oxidizing. They measure 5" x 24". This seat has stainless steel inserts at either end of the seat and there are 4 washers, ½" thick, welded to each insert and then molded into the rubber. The seat should last 2 years in harsh conditions and up to 5 years in optimal conditions. Some conditions may require replacement sooner.