First-time buyers often ask: how are casters added, and which kind? Casters usually come as two swivel and two rigid; the swivel ones can carry a brake. They split into light-duty and heavy-duty: light-duty carries less, uses thinner material, and costs less; heavy-duty uses thicker material and costs more. Common caster sizes on warehouse cages and metal returnable containers are 4, 5 and 6 inches, with 5-inch the most common. As for installation, there are two options: the customer welds the casters on themselves, or the manufacturer drills the holes and the customer bolts them on. Why does not the manufacturer just weld or bolt them on? Once casters are fitted, the cage cannot fold and nest for shipping. That means more space and higher freight, and the casters themselves get damaged in transit. So customers usually fit them after delivery.