The Squirrel Buster Mini is guaranteed to be squirrel proof.  The openings in the bottom of the metal mesh shroud are aligned with the seed tray and allow the birds access to the seed.  When a squirrel climbs onto the feeder, its weight automatically forces the shroud down, closing the access to seed.  Squirrels are shut out, but not harmed in any way.  Both perching and clinging birds love this feeder.  The tension is not adjustable on this smaller version of the Buster, but this is a great feeder at this price point.  For maximum features, see the Squirrel Buster Plus.