The Need for Clearance
Remember it is the squirrel's weight that triggers the closing mechanism so if a squirrel can reach over from a nearby foothold and avoid placing its weight on the feeder, it will be able to access the suet cake. This is why you should allow for at least 18 in. / 47cm. of clearance around the feeder. This will force the squirrel to climb onto the feeder triggering the closing mechanism.
Negative Grip Tube
The Negative Grip Tube prevents squirrels from grasping the wire hanger with their hind legs, hanging down alongside the feeder and defeating the closing mechanism.