This is a "squirrel resistant" or "squirrel proof" bird feeder designed to mount on a 6" (well, more like 5.5") wooden fence post.

Hardware needed is a couple of screws to hold the arms to the box (loosely), and two screws to mount the box to the post (just use the top two holes as the lower ones interfere with the new arms). Optionally, you can also drill a hold in the back arm of the lid so that you can secure it to the post.

The lid slides on from the front to "lock" it to the box.

This is now the third iteration. The changes are really all centered around the arms. I found they were too weak and were breaking after excessive squirrel abuse. Also the spring system was never very satisfactory. I tried, but plastic springs don't have much longevity. I have now shifted to a counter weight system. Just place anything with enough weight on a wire and attach it to the back of the arms. There is a decent view in the second picture.