The sanding cap burs are very efficient on callus and they are disposable.  The sanding paper caps slide onto the rubber bur.  For most drills use the 5mm to 10mm sizes. The larger sizes are for very strong drills and even then keep the speed below 10.000 rpm due to wobble.  Ceramic burs are used to smoothen rough nail and polishing burs produce a nice shine on the nail. All burs here can be used dry or wet.