It's all about terminology folks... flat head philips is appropriate when referencing a machine screw.
I'm guessing that by "spring washer", he means a split lock washer?
Lastly, I'll offer 2 cents on the design... I would include a hollow threaded stud in the adapter. Then secure the mirror with a split lock washer and a nut instead of a hollow bolt. The nut can be tightened with a wrench, with the wires in place.