i thought i had already replied to this thread but anyway, My 2 cents is always grind a flat.. ive used a drill and drilled a small dimple before also, my 16 cell BL setups will only go about 2 feet before they slip if you don't have a flat on them.. it takes 10 seconds to do it and i think if only done just enough it will stop the coupler from ever slipping, also in most cases it allows the set screw to sit deeper and have a better bite in its thread