"Credit Card" Diamond Sharpening Cards Available in extra fine, fine and coarse grits, pocket-sized diamond sharpening cards encourage keeping every edge tuned to its utmost. Using only water for a lubricant, knives can be drawn across the stone at a 20 degree angle, while router and other bits get their flat sides sharpened. The monocrystalline diamond structure of these cards is exceptionally strong and doesn't break away under use. One of the medium or fine cards in a shirt or apron pocket can take a lot of the tedium out of caring for edged tools. Cards are 2" x 3-1/4".