Expanding rubber stem casters are designed to mount the caster into round or square tubing.  Turning the hex nut beneath the lower raceway on the swivel caster expands the rubber stem adapter inside of the round or square tubing for a tight fit, as shown here. Caster City offers various expanding rubber stem sizes.

Caster City manufactures expanding rubber stem kits to fit an Inner Diameter range of 3/4″ to 1-13/16″ Inner Diameter metal tubing.  See the chart below.

We manufacture all stem casters in Stainless Steel as well.