StarTech.com Caster Kit for Open Frame Rack - 4POSTRACK Caster Kit for Open Frame Rack - 4POSTRACK Add mobility to your 4POSTRACK series open frame server rack with these heavy duty casters Compatible with the 42U Adjustable 4 Post Open Server Equipment Rack Cabinet (4POSTRACKBK) Four post rack / 4 post rack / 12U 4 post rack / 12U server rack / 12U open frame Compatible with the 42U Adjustable 4 Post Open Server Equipment Rack Cabinet (4POSTRACKBK)