>>>*Starrett, those are straight. Most typical squares aren't.

*One small area that is off a thousandth of an inch can equal several thousandths in warpage of a casting. Those tiny hard to see spots are close to number one for early gasket failures.

I also use a small dead straight edge for close checking around bores, etc, with a bright light behind it.......*EB

*Beats the he** outa me!....*LOL**...