The old 3 inch casters are frozen. When I try to remove them with a long socket wrench, the bolt (threaded stem) just turns. There is no way to get a grip on the other end to prevent this. The space between the bottom of the cart and the wheel is too small to get a wrench on that side of the bolt.
Some manufacturers make specific wrenches to remove casters. They are basically flattened wrenches about 1/8" thick. If you have the manufacturer of your caster you can call our sales team to determine if there is a caster wrench available to help you out. 1.888.388.6372