■ → Spring-loaded design, which can be opened and closed freely by automatically adjusting the height on uneven ground while eliminating gate sagging ■ → ø100mm (4 inches), height retractable 30/60mm, swivel casters, wheels with side brakes, wheels with brakes available ■ → heavy duty casters, the maximum carrying capacity of 440 pounds or even withstand exposure to chemicals and solvents ■ → Shock absorber, galvanized with high-quality steel surface, oil and rust proof, easy to move and rotate, easy to open and close the door ■ → The appearance is noble and elegant, cost-effective, suitable for irregular terrain, factory doors, garden doors, warehouse doors and other occasions.