Genuine Arkansas Black Surgical (Ultra Fine) Slip Stone Whetstone for Sharpening Carving Tools 4 " X 1 5/8" with 1/8" and 5/16" Radius BAS-14-P Slip stone for sharpening carving gouges, molding plane blades or any concave edge Slip stone is 4 long by 1 5/8 wide, One edge is 1/8" diameter and the other is 5/16  diameter. This is the hardest of the Arkansas stones and will hone a polished, very sharp razor sharp edge Color can vary from dark grey, to blue/black to black. Genuine Arkansas stone is 100% quarried in the Ouachita Mountains of Central Arkansas