I bought a set of these skates:
MADE IN USA 12,000lbs Machine Dolly Skate Machinery Mover Machinery Roller | eBay
They are made by a guy up in Ohio. You won't be sending your money to the ChiComs.
As far as Mr Bridgeport's comment on recommending Hillman over these- forget it. I have used the Hillman skates many times These work better. I hate Hillman skates.
The few machines I have moved with mine had open holes in the base, i guess for bolting to a skid. I just put a long bolt through the hole and threaded into top or the skate. This eliminates the issue with having 4 skates and loosing one. 3 skates does not always work, My mill for example has 4 pad corners and very big relief between. Another thing I have found handy is to buy some thick soft rubber from McMaster and put between the skate and the machine pad on 2 of the skates. This tends to keep them pointed in the same direction a little better. Then you can use the other two skates for steering.