Originally Posted by 2manybikes
Using washers will allow you to use any length screw you want without drilling.
The screw hole on the light is actually threaded, but you can't see it without a bright light. It is a tight interference fit to lock the screw in place.
You miss the point; by drilling the existing hole deeper you are able to more deeply seat the screw and create a stronger mount. If you are only using the 1/8" deep hole as it comes stock, then a good whack is all that it would take to tear it right off the back of the rack.