Built-in Spring Design: Innovative spring built-in-design, extends springs service life while providing a more beautiful appearance. The built-in spring-loaded clamp acts as a shock absorber when the gate wheels for wooden gate roll over uneven or rough surfaces, reducing stress on the gate hardware and extending the life of a gate"s posts and hinges Spring-loaded Gate Caster: Adjustable spring bracket with up to 1-3/4 spring-loaded vertical travel, automatically adjusting gate height with surrounding terrain throughout the opening and closing cycles, effectively prevent gates from sagging to keep the fence line levelrong load bearing support, 220lb maximum load capacity for each gate caster, make it easy to open or close large, heavy gates Heavy Duty Gate Wheel: Thicken matte black power coat finish plating steel plate and double ball bearing bring strong load bearing support, 220lbs maximum load capacity for each gate wheel with side brake, make it easy to open or close large heavy wooden gates, vinyl gates, metal tube gates or metal swing gates 360 Swivel Fence Gate Wheel: 4 inches ageing resistance rubber caster with 360 rotation top plate, great in mechanical strength and loading capacity, easily transform to any direction that you want, enables you to spend little strength to move gate safely