I've built two of these but can't remember off hand what sizes I used. It's all small drills so you might be better with a number drill set (1-60) instead of a fractional drill set. If you only have fractional sizes then convert the fractions to decimals (i.e.: 1/32 is equal to 1 divided by 32) Take the decimal you wind up with (or the decimal printed on the drill set) and you will be able to find the number drill that corresponds to the Millimeter size you need. Just remember that 1MM is approximately equal to .040", 2MM would be .080", 3mm =.120", 4mm=.160" and so on.

The actual value of 1MM in inches is .03937", not quite .040" so the bigger you go in MM the greater the error will be. For instance, 10mm is equal to .3937". Converting as I described above would give you a number of .400". The error between the two is .0063" or a little thicker than 2 human hairs, certainly nothing to worry about when drilling holes in wood.