Norton India Stone - Medium 8" x 2" x 1"

A medium India stone is only one of two oilstones you really need. Hone the back and bevel of the cutting edge to form a wire burr on the India stone. Then switch to a hard Arkansas stone to hone and "chase" the burr until the wire edge is gone. Finally strop on plain leather for a shaving sharp edge. Of course there is more to sharpening then that but from a sharpening stone point of view it's pretty straightforward. Oilstones should be used with oil, not water, or they will clog, but otherwise the India stone is pretty indestructible. You should never have to flatten an oilstone. Twenty five year old India stones in daily classroom use are still perfectly flat. If you see a cupped artificial oilstone it is probably a Crystolon stone which is a lot softer. 8" x 2" x 1".