Mills: 25, 30, 45...Distinctions | The HobbyMachinist
With the 45 number it's usually referring to a larger bench top mill drill with a square column that was originally made by Rong Fu, hence athe name, RF30, RF40, RF45, etc. But for the 30, there's Rong Fu style RF30 mill drill with a round column then there's the BF30 style mill drills that are are a bit smaller but have square colums.