I used 50mm (2") and recessed the bottom panel of the cabinet so they didn't stick out too much, probably 20mm and found it rolls OK but is not overly responsive so when I'm caning the controls it doesn't move around too much. I also used the locking type on the front for this reason but due to the weight of the cabinet, I probably didn't need to do this as it don't move at all, the Castor's seem to be handling the weight of the cabinet fine.