3-stage knife sharpener for kitchen PREP (MIDDLE) SLOT: The first stage uses hard diamond rods to pre-grind steel blades that have fallen out of shape. Only this grinding stage has the necessary hardness to restore blunt steel knives to the required basic shape before proceeding to the next stage. SHARPEN (FIRST) SLOT: The tungsten steel step is for grinding normal steel knives, making them sharp again. FINISH (THIRD) SLOT: The final step of the sharpening process. Honing the knives with a ceramic stone to remove burrs and polish the blade. Durable & Easy to Use The sharpeners are made of stainless steel and ABS plastic, which are durable, have a long service life, and can fully withstand the pressure generated during sharpening. How to use the kitchen knife sharpener Place knife sharpner on a firm table. Put the edge to be sharpened in the middle (PREP) slot. Pull the edge backwards towards you in one direction few times. (Make sure the edge is pointed away from you). Then repeat above steps for first (SHARPEN) slot and then third (finish) slot.