Concave Deck Mount Hinge - Black is made of delrin acetyl resin compound with a stainless steel machine screw to except a socket end. Designed to be mounted on 7/8" tubing. Delrin has excellent resistance to corrosion of any kind and is unaffected by water exposure. Colour is cast in, not coated on which means that it hides scratches well and are self lubricating to a degree. These fittings are injection moulded under high pressure to give excellent tolerances in a lightweight, economical product design for durability and performance.