Equip your semi to be Ready for the Road Ahead , with the Whiting 87" Aluminum Roll Up Door Balancer Assembly, a key component to provide your semi with a smooth and reliable spring-operated door assembly. To prevent your roll up door from slamming shut or opening at lightspeed, this replacement balancer assembly is crafted with stable weights that streamline opening and closing. Crafted with rust and corrosion-resistant metals for long-term durability in humid climates and rugged conditions. FleetPride is your First Click in Heavy Duty .