This is one of the first MAC sharpener designs.  This coarse grit stone should be soaked in water for 2 minutes before use.  Use it like a file and slowly work your way up and down each side of the blade.  The "foot" near the handle helps to gauge the proper angle.  250 grit.

Advantages: Inexpensive.  Works on almost any straight-edged knife (including other brands).  Coarse grit quickly resharpens knives that were extremely dull.

Disadvantages: Requires proper technique to use effectively.  Wears out after lightly sharpening 50-100 knives or heavily sharpening 10-20 knives.

UPC: 854911000631