[Integrated Spring Design]: Innovative integrated spring design extends the service life of the spring while providing a more aesthetically pleasing appearance. Built-in spring clips act as shock absorbers when wooden door wheels roll over uneven or rough surfaces, relieving stress on door hardware and extending the life of door posts and hinges [Spring Door Casters]: Adjustable spring brackets with vertical spring travel up to 1-3/4, automatically adjust the height of the door according to the surrounding terrain during opening and closing, effectively preventing the door from sagging to keep the fence line level [Heavy Duty Door Wheels]: Thick matte black finish electroplated steel plate and double ball bearings bring strong load-bearing capacity, each door wheel has a maximum load-bearing capacity of 250 pounds, making it easier to open or close large and heavy wooden doors, vinyl doors, tubular metal doors or metal revolving doors [360 Turnstile Door Wheels]: 5-inch aging-resistant rubber casters with 360 rotating top plate, excellent mechanical strength and load capacity, can be easily converted to any direction you want, and can safely move the door with little effort [Easy to Install]: Heavy-duty universal mounting plate with 3 holes, can be easily fixed to wooden doors with lag bolts. Versatile hole pattern also allows for easy installation onto tubular farm gates along horizontal or vertical gate tracks, with mounting bolts and screws included