Sharpens the inside of square chisels with a six flute HSS cutter. After sharpening the inside, you deburr the four outside faces using the flat diamond stone supplied. Chisels should be held gently in a vise, and when using the HSS cutter in a power drill use caution to ensure that you don't sharpen the entire chisel away! The kit includes four guide pins of common internal diameters to align the HSS cutter with the inside of the square chisel. There is simply no other way to successfully sharpen mortise chisels. An essential accessory for anyone who uses a chisel mortiser.