On Sat, 14 Dec 2019 22:06:15 -0500, Alex wrote:

Clare Snyder wrote:
On Sat, 14 Dec 2019 16:16:23 -0500, micky
wrote:

In alt.home.repair, on Sat, 14 Dec 2019 11:33:58 -0500, dusty
wrote:

The box itself is bolted to a 4x4, then this goes into a patented flex
adapter that allows the top 2 feet of post and the mailbox to flex if
anyone touches it. The bottom 2 feet or so then feeds into a 4x4
bracket that is bolted to a concrete sidewalk at the four corners of the
bracket with 5/8" lag bolts and lead anchors in the concrete.
Instead of bolts and lead anchors, you should use molly bolts.

Drill a 3/8" hole into the ground until you get to the hollow part, and
that will determine how long the screws should be.
Same thing as what I recommended - Molly was one brand I missed.
Basically a wedge anchor bolt.

3/8"? Molly bolts?

Look at my two suggestions and add an epoxied threaded rod to that.
IIRC you can get the hilties in half inch