The first thing I did upon receipt was check the square. All inner and outer surfaces were bowl-shaped and curved. A few minutes on the belt sander and I removed the restraints. Mine were all square but I would have had to sand too much material to remove all the cups. These squares are heavy duty and good for general positioning, but aren't quite right for precision work. I wouldn't use them for picture frames without finishing them first. They're about what you'd expect for the price I think.