SPRING LAODED DESIGNDesigned to allow gates to open and close freely by automatically adjusting height on uneven ground while eliminating gate sag and shock absorption. HEAVY DUTY CASTER 4" rubber rate caster has a maximum load capacity of 132lbs and can also withstand exposure to chemicals and solvents. PREMIUM MATERIALSswivel caster is made of high-quality rubber material, which is durable to use. Metal caster stem, double support bearing, not easy to wear out, and easy to clean. 360 DEGREE SWIVEL spring loaded gate caster can rotate 360 degrees and it can glide smoothly over hard or smooth surfaces such as concrete with little resistance. It can be mounted on wood, metal or vinyl doors. EASY TO INSTALL fence gate caster have a heavy duty general mounting plate with 2 holes. It can be easily connected to the wooden gate or along the horizontal or vertical guide rails of the tubular farm gate.