"DIYGUY" wrote in message

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 ...

Load factor is one thing. Yes, the 150# caster is able to take the total
load of 600# assuming equal distribution.

Size is a whole 'nuther factor. I'd not use less that a 4" caster for a
tool stand. To put this into perspective, go out to the curb in front of
your house. What will go over the curb easier, the 27" wheel of a bicycle
or the 6" wheel of a baby carriage? Smaller wheels are more likely to get
hung up on a wood chip than a larger wheel.