A/W-3 is designed with 4" wheels to give you an option to wheel heavy solid wood or steel core doors from on location to another.This door holder will clamp light hallow cord doors. For these kinds of doors it must be locked manually to avoid any unsteady movement6s. On solid core doors you don't have to lock it because the weight of the door automatically clamps the door on place. Simply make sure the wheels are unlocked with the leveling rest in the forward position. Place the door centered and balanced on the Denpo Door Holder and you're ready to roll!