Don't know how to loosen a hex head screw of strange dimensions? None of your hex keys can be used, is it too small or too big? Probably have something to do with the imperial-inch screw.
But you don't have to buy a whole set of inch-allen keys - but just the one you need. The table below can help you choose the right one.
|APPROXIMATE DIMENSIONS IN MILLIMETERS||DIMENSIONS IN INCHES|