Thinking back to my days working in the factory at Boeing, one of the first things I learned was all inside corners on an airplane are rounded. You will not find square inside corners anywhere on a plane because that is the beginning of a crack or break. Same principal applies to diamond mold chips. Over the years I've received exactly two broken chips in the mail and both times they were diamond mold chips.

Need to make sure those chips never get near the rollers of the USPS' automated equipment and you can cover the envelope with non-machinable surcharge stamps and stamp hand cancel only on the front and they will still try to machine it.