There's also a pic of one of my lathes on them.
These work very well. You don't have the problems of normal skates on uneven concrete, where you're pushing the machine and realise one of the skates has been left on the ground and has rolled out from under the machine.
Once loaded up on these skates, the machine can be easily moved by 2 guys. Sometimes some gentle persuasion with a large crow bar is needed if you hit a large concrete gap or height difference.
Mike