.... answer me this question. If a caster wheel is rated at a load
carrying capacity (which it is) how is the rating determined? I have a
600# tool I want to put on casters. Does each caster have to be rated
at 600# or can I get four casters, one on each corner, that are each
rated at 150# (or more) load bearing capacity?

This is important because casters with higher load bearing capacity are
much larger and I want to keep the added height of the tool down to the
bare minimum. Thanks all for your answers ...