These expanding mounting stems install into the open holes on compatible bolt-hole casters. When the casters are installed in metal tubing and tightened, the stems expand to keep the casters firmly in place in the tubing. For best results, the diameter of the expanding stem should be as close as possible to the diameter of the mounting hole on the caster and the interior dimensions of the metal tubing. Bolt-hole casters (also known as hollow-kingpin casters) and expanding stems are used on carts, racks, retail displays, furniture, and other equipment with frames made of metal tubing. They allow the equipment to roll, which reduces the effort it takes to move or reposition it.