2" Castor Add on with 2 locking wheels and 2 regular wheels. This will make moving your racks a breeze. Easy rolling and durable, able to hold up to 250lbs with a set of 4. If you are keeping racks in a basement or on concrete flooring this is a fantastic way to help with keeping temperature in your lower tubs. Need more than castors for a colder room? message us about insulation choices to be added to this option