The DMT Diamond Honing Cone is a tapered diamond slip stone for sharpening gouges, turning tools and other curved edges, in fine grit (25 micron, 600 mesh). It comes in three sizes: Small with Handle, Medium and Large.
The Small tapers from 3/8 to 1/8 in diameter over a 4 in cone and has a 4 in handle. The Medium tapers from 3/4 to 3/8 in over 6 in, and the Large from 1-1/4 to 3/4 in over 8 in; both are half-round, with the diamonds on the convex side. DMT's monocrystalline diamond surface cuts faster than conventional stones and needs no oil: use it dry or with water.
DMT, short for Diamond Machining Technology, was founded in 1976 by aerospace engineers. It started out making grinding wheels, and its first hand sharpener was made from the center punched out of a diamond grinding wheel. A buyer at L.L. Bean tested an early sample and worked with DMT's engineers to refine it. Acme United bought DMT in 2016, and DMT is based in Marlborough, Massachusetts.