Does anyone know what tool (is it slotted, hex, etc.?) is needed to tighten the retainer nut/screw that faces the windshield? Because the windshield is so close to the mirror mount, there is not much room to see what is in the hole that looks like it would tighten the rear view mirror mount, unless their is another way to tighten the mirror mount to the glass. Any assistance would be greatly appreciated.