According to two of my 306es, the threaded hole at the back is open. The bight control screw goes where the set screw now resides. Penetrating oil should help; after it soaks for a day or two, try heating it up with a blow dryer when you attempt to remove it. Are you sure that's a set screw? Could it be the bight screw snapped off?
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Last edited by Manalto; 08-22-2015 at 07:58 AM.