There is a small board on the inside of the container. From the bottom side, there are screws, with washers, screwed up into the board - and one of the screws goes all the way up into the limb.
The board gives it a base for stability. (I actually just added the second screw to the other end of the board the other day to stabilize it a bit more....just the one screw held it up okay, but it had a little bit of give to it....)
There was also glue between the board and the end of the limb.
The board inside....
The screws from the underside....
Snoopy (the green cheek) and Woodstock (the sun) sitting around here with me...