Been there.i bought some ' snappy 'drill replacements from Axminster and they were too short. Found some extra long bits on amazon for buttons .There are different size centre drill guides of course so always measure before buying the drills.I use the Trend centering drills and think the one I use most is the middle sized one which is 7/64", the bits are extra long though so standard bits won't fit, I get the proper Trend ones, probably different for other brands.