Prepare your semi to be Ready for the Road Ahead , with the Whiting 4" Steel Roll Up Door Roller Hinge Assembly that provides your vehicle with a smooth and reliable spring-operated door assembly. With a flexible design that rotates as needed, this replacement hinge assembly is the ideal choice to keep your roll up door opening and closing with ease. Manufactured with corrosion and rust-resistant metals for extended use in harsh conditions and humid climates. FleetPride is your First Click in Heavy Duty .