Wiki-Medium Whetstone

Among the three types of whetstones, the fineness of grindstone is medium. In the case of synthetic whetstones, the #400-2000 grade is often used. After grinding the blade extensively with a rough grindstone, a medium grindstone can be used to make deep scratches on the blade shallower and the surface smoother. The medium grit is also fine enough to produce a sufficient sharpness even if sharpening is completed with only this medium grit, unless the shape of the blade needs to be drastically deformed, such as for repairing a chip.

Related websites
Mastering Japanese Knife Sharpening: Techniques & Tips | KIREAJI