Can't build a machine without this stuff! Use on axis drive pulleys at the motor shaft and the ballscrew/rack end. Put a dab on the inside of the pulley and install it. This stops the pulley from working loose over time (set screws and flats can't take long term CNC use..they work themselves loose, this stops that!) Its always best to have a keyway that is fitted perfectly but 620 really does the job. Also used in sleeving shafts to increase thier diameter , adapters, bearing setting etc.