I got the initial spacing by taking a piece of aluminum foil and pressing it up against the disc to get an impression of how far apart the holes were.
Nice tip, that one is going into the mental tool Box.I think my mental toolbox has too many holes in it
Do yourself a favor and forget the screwdriver. I found it a major pain. Spend 15 minutes or so and made one of these. Now I fiddle with the adjustment alot because it is so easy. My 2 cents.
Wayne