Stop in for a cup of coffee
I have broke many of those also. In my case, they are strong enough to hold what they claim (or reasonably close) just don't try to move the object as the casters never work as they should. Something will break - you or the cart/dolly/etc. I had a 460/C6 combo on 3 of those 4 caster dollies. They are rated at 1,000lbs each. Broke them all when the casters wouldn't swivel, bent sideways, and broke.
