I use the springs and small washers from this package: http://9spuzzles.com/index.php?gOo=good ... oductname=
Unfortunately, the big washers and screws are no good. They force you to design center holes much larger than regular M3 screws which results in a much larger puzzle overall. If you do want to use those screws then a 2.75mm hole will be fine as well.
I use M3 screws from Fabory and combine them with those small washers and springs from 9s.