All hardware is internal. Four stainless steel washers are welded to a 301 full hard stainless steel insert that is molded into the seat. The insert is covered with EPDM material that helps withstand harsh weather and fading. EPDM: Ethylene-propylene-diene-monomer is a synthetic rubber material which helps prevent crazing, cracking and oxidizing. Natural rubber is often made from recycled tires etc, and you are never sure what the actual rubber. Measures 6" x 24" x 3/8" thick. 3.25 lbs.