To further what Mike said "holes where you need them"

Examine the actual retract mechanisim. You will notice the pushrod from the servo moves a rod from full up and locked to full down and locked. If the rod's full range of travel is 1" then you drill the two holes so they are 180 degrees apart on the wheel, and 1" apart with a line between the two going through the center of the servo screw. Substitute whatever measurement that your mechanisim uses and you will have perfect retract servo throw.