Japanese 4000 grit multiform slipstone.
This traditional Japanese waterstone is for the final fishing of edges of a wide range of wood carving tools.
On one edge the radius changes from 13mm(1/2") to 3mm(1/8") over its length. The opposite edge is tapered at an angle of about 40° making it ideal for sharpening the inside of parting tools.
Size 106(4.1/4) long x 50(2) wide x 9.5mm(3/8") thick.