Note: As of February 2011 the RA22CS-S is now designed to accept #6 screws.
Strong countersunk ring magnets sized specifically for #6 flat-head screws. The south pole is on the side of the magnet with the large hole, where the head of the screw would be.
These countersunk rings can be used for a wide range of applications including door closures and tool hangers.
For even more strength, consider using with NSCA2
Steel Cups, which can more than double the pull force.