It's only for a slab with the small steel casters I used. A 3/4" rod goes through the box tube at the base and is plug welded to the box tube the casters are welded to. 1" round is welded to the 3/4" bar so 3/4" rod will slip in and out (store them with the iron workers below), to be removed when the table is in the down position. A section of angle iron in the center holds the table up when you want to move it. A small tab below the angle iron section keeps the rod from diving to the floor if/when the casters have to ride over something on the floor.
The problem with casters is that they allow the bench to move too much if you ever need to do any twisting, like is common when you have a vice or iron workers on it.