Well a dremel tool is always my first suggestion in this matter. However; I have another, cheaper, solution. You'll need: CA/Super Glue, and a hex wrench. Step one: place a few drops of CA/Super Glue into your galled hex head bolt. Step two: Place your hex wrench into the hex bolt and let the wrench bond to the bolt for the recommended curing time of your particular glue. Step three: Twist that sucker out of there and you're home free!