The JewelStik Diamond Sharpener is the original oval shaped, two-sided diamond sharpener that Chefs have been using for over 30 years. These sharpeners are offered in a variety of lengths and widths to help you determine the best for your application. The rule of thumb is your sharpener should be at least as long as your blade. The oval shaped steel helps you hold a good angle (generally from 18 to 22 degrees) on the edge of your knife. The diamond surface is on both sides of the sharpener.