These chisels, available only in a set of 5, are made from a special alloy steel, similar to high speed steel, laminated to a softer steel base. The harder edge steel, approximately HRC 68 will better withstand continual use on particle board and knotty timbers. Sharpening procedure is the same as for other Japanese chisels. Sizes are 9, 15, 24, 30 and 36mm.