EDR wrote:

Any suggestions/recommendations on where to acquire square holes?

Most woodworkers can make these. They're called mortises. The old-fashioned way to
make them is to drill out the center and chop the rest out with chisels, but there
are mortise cutters for use in drill presses.

George Patterson
In Idaho, tossing a rattlesnake into a crowded room is felony assault.
In Tennessee, it's evangelism.