I used a heavy 2-1/2 inch steel wood screw to secure the plastic hollow square post for the mailbox to the cemented-in pressure-treated 4x4 anchoring it. It was far easier to get a good bite on the slot-headed screw than it was a Phillips (which I had managed to strip out with the drill's screwdriver bit). When the going got hard, I put a wrench on the shaft of the screwdriver and leaned in to keep it in the slot. Worked pisser.