It needs to be a size (diameter) smaller than the outside thread (major Diameter) but as large or slightly larger than the minor diameter. This worked but the drill always seemed a little big for the job and sometimes getting the chuck to clear the tuners and the end of the dulcimer required some hand drill … Now, most tuning pegs can be a simple process of removing the old one, putting the new one in the hole and re-drilling the screw hole/ mounting tab if needed – this is all assuming you’ve just bought direct replacements and have done your homework and measured the size of tuning … 3. I have the specs, and i am trying to avoid drilling any new holes. For years I drilled these with an “eggbeater” hand drill. I'm changing out tuning pegs, and I was wondering what is the best technique for drilling the mounting screw hole (back of the headstock). Put a dab of bees wax or bar soap in the hole … These set screw holes … I was thinking of installing the tuning key then align it, then drill the little pilot hole using the tuning key mounting hole … Drill a pilot hole. The screws that hold the tuning machines in place are very small and require small pilot holes. Important note: We do not drill holes for the small set screws or pegs for tuning machines, due to the fact that there are so many different models and styles of tuners on the market, and most of them have different locations for these holes. Mark the hole with a pointed awl to give it a good start. Im trying to find an aftermarket, upgraded, premium (18:1 or better) set of 3+3 tuning machines to replace my old factory winders on an acoustic.