This would be a PD6 - Post Doctor 6x6
There is a "lip" at the top of the piece so if it's a tight fit that slides on all 4 sides, probably not. If it's a vinyl mailbox then possibly
It works for a nominal 4x4 so 3.5 x 3.5
A nominal 4" x 4" is actually 3.5" x 3.5" This will fit perfectly
If it's a mailbox, it doesn't matter what side you mount it on. If you have a fence attached, there's only one way of course.
I do not think so. It requires putting screws into the wood to hold it up right.
No, needs to be broken at ground level
one, box has all the contents needed including the drill bit.