Three years of field testing made this Squirrel-Proof! Our Squirrel Blocker™ 1 by 1" fencing and the distance to the 1/4 by 1/4" stainless steel wire feed tube is the formula that stops squirrels cold. The open flow-through bottom insures no seed collects to attract hairy hangers-on that drive birds away. Birds perch all over the Blocker fencing and put their heads through it to pick a seed from the seed-saving mesh tube. You will find that seed lasts longer in this feeder -- birds take one black-oil seed at a time! And squirrels just give up!