For large platforms, or entire table tops, these bearings are the best choice.
The two smaller sizes have die-cast aluminum raceways (1/2" total height), while those of the larger sizes are machined from solid plate (5/8" total height). Load capacities are 110, 180, 275, 660 and 990 lb respectively.
All have five or more removable plastic feet for making portable platforms; removing the feet allows them to be permanently mounted (three largest sizes require drilling). All have full races with more ball bearings than we wished to count.