Approx 1/8”.

The one I saw they left open while for sale.
Would assume allowing prospective buyers to do their own poking around or to convince doubtful sellers.

As I said earlier, I use the plastic handle of screwdriver for the tap test.

Good/solid wood sounds like your tapping the chrome bumper on a ‘68 Caddy.

Bad/soft wood sounds like a plastic Honda bumper.

Very apparent.