1. Place your knife’s blade along the crease of a manila folder.
2. Mark a line about ½ inch from the tip of the blade and another about ½ inch from the spine.
3. Using these marks as guides, cut the folder into a rectangle.
4. Staple the top half and side of the rectangle at ½-inch intervals, leaving the back end open to slide in the knife.
5. If the handle of the knife prevents the guard from fully covering the blade, snip the opening at an angle to accommodate it.