Mine are 3/8" apart, but that won't make a big difference--1/2" will work just fine.
If you are using a standard straight board (where you have a "W" when you wind off a strand), the length holes need to be 1/2" apart.
I strongly suggest using instructions for a jig that lets you go by string length instead of bow length. Not all bows of the same length get the same length string. Some 66" bows will get a string 64.5" long, some will get a string 59.5" long, or just about anything in-between.
Chad