"Michael A. Terrell" wrote in news: snipped-for-privacy@earthlink.net:
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A box cutter is a flat hollow rectangle of metal with a flat rectangel of metal that slides inside. The inner rectangle has notch where the top of a single edged razor blade sits and a triangular section removed at the front so that a small part of the blade is exposed. You push on the back end of the device to expose the bit of blade and push it back in to cover the blade when not in use. It has been used in stores for decades for unpacking boxes...