The Spyderco 302 ceramic sharpening stone ultra-fine, 302UF is a top-quality ceramic stone made from aluminium oxide (synthetic sapphire) to sharpen knives and other tools. The advantage of aluminium oxide is that you don't need water or oil and that it is so hard that even after a long time sharpening grooves won't appear. You can also easily sharpen hard metals with this stone.
This is an ultra-fine stone that is great when polishing and finishing your already sharp knives. You can actually sharpen your knives on a medium or fine Spyderco sharpening stone.
On the Mohs scale these stones have a hardness of 9.2. To compare, diamond had a hardness of 10.
The sharpening stones can safely be cleaned in the dishwasher or autoclave, but you can, also easily clean them with a little liquid abrasive or a Lansky eraser block.
The sharpening stone comes in a plastic storage case. This case can also function as sharpening stone holder!
The grain for Spyderco ceramic sharpening stones are measured in micron, which corresponds with a specific grain. Unfortunately the United States and Japan each use their own system. Japan uses the JIS R 6001 method and the United States the ANSI method.
Below a small overview:
The Spyderco Medium stone is 20 micron, grain J600 in Japan and grain 390 in the United States.
The Spyderco Fine is 6 micron, grain J2200 in Japan and grain 1000 in the United States.
The Spyderco Ultra-fine is 3 micron, grain J4000 in Japan and grain 1300 in the United States.