The Fallkniven FS4 is a super cool sharpener that is as handy as it is unique. Utilizing 25 micron diamond particles on one side and 1 micron ceramic grit on the other the FS4 is all you need to sharpen your knife in the field or at home. The sharpening surface (looks like a blade) deploys like an automatic knife with the push of a button. Yes, we admit it...we like the Fallkniven FS4 because it is really neat. But like all Fallkniven products, it is high quality and works incredibly well.