Mirrors still move even when bolts are tight


I see what you mean now. The center of the bolt has that raised section in the middle that butts up against the bottom of the stem...putting the washers on would allow the bolt to pull the stem down tight into the mount, thus holding it firmly in place. I will pick up some washers that fit into the bolts. Thanks.
 
Right but take a mirror stem and measure it Heck hang on! Ok the stem is .390" so depending on the clearance a 3/8" split lock washer should do it. If not 7/16" will. But I am betting I used 3/8" because there is a radius on the stem shank.
 
I used lock washers on mine very simple do as Warp says so they fit over the mirror stem