Boker Sieger Long Life Sharpener, 09SR001. This sharpener, made of synthetic ruby, is 20 times harder than hardened steel (20,000 Knoop hardness, which is roughly a 200 hardness in Rockwell units)! The most unusual aspect of this sharpener is the high efficiency (taking less time for sharpening), in combination with an extraordinarily fine edge, allowing superior edge retention. In addition, this sharpener will last longer than a diamond sharpener, as it is not a coated instrument but one of bulk material. Can be used either wet or dry, and can be simply cleaned with a dish sponge. Length: 8 Inches.