Bolt Hole Casters
Racks, carts, furniture, and other equipment can be fitted with bolt-hole casters to allow them to roll, reducing the amount of effort necessary to move or reposition the equipment. They're also known as hollow-kingpin casters since they include an open hole that allows for more flexibility when mounting them to equipment. The casters can be mounted in tube with corresponding expanding stems that get larger as they're tightened to keep the caster firmly in place in the tubing, or they can be installed in wood with a lag bolt of the appropriate length and thread.