Measure the diameter of your tuner's mounting nut (shown at the right); this is the required tuner hole diameter, which is quite likely to be 10mm. Drilling the tuning machine holes is usually done on a drill press but can also be done by hand.
To ensure that the holes are perpendicular to the peghead surface and to get the alignment and the distances between the holes right, I used a self-made drilling jig. It consists of a 2x2x6" (50x50x150mm) hardwood block with three 10mm holes whose centers are 1-5/8" (42mm) apart and 13/32" (10mm) from one long edge. I have to admit that I went to a drill press for making this jig. A guide made of plywood glued to one side makes it easy to correctly align and fix the jig on the peghead.
The middle of the first tuner hole should be located 2-3/8" (60mm) from line "B". Position the jig and remember to put a backing board on the back of the peghead before fixing the jig with two clamps. Make sure that the clamps stay clear of the tuner holes.