The Suehiro tapered gouge stone is a Japanese water stone shaped for sharpening gouges and carving knives, in 280, 1000 or 4000 grit.
One face is convex and the other concave, so you can sharpen both the inside and the outside of a curved edge. The stone also tapers along its length to fit different sizes of tool. It's 152 mm (6 in) long, narrowing from 57 to 20 mm (about 2-1/4 to 3/4 in) wide and from 30 to 14 mm (about 1-3/16 to 9/16 in) thick.
Use the 280 to take out nicks and chips, the 1000 to sharpen and the 4000 to hone.