Norton 4000 Single Grit Waterstone. Size 8x3x1 inch.

This stone is used for premiere sharpening of Your woodworking tools. The stone should immense in water for at least 10 minutes before use and kept wet during sharpening. With this stone You achieve an almost mirror finish, and the finest edge. Use this stone prior to honing on a 8000 grit stone and after having worked up an edge on a coarser stone (220-1000-1200 in subsequent order).

The 4000 and 8000 grit stones should be used as complement to either coarser watersones or diamondstones.
After having practiced sharpening on these stones You will appreciate the edge You receive and the increase in working pleasure this gives You.