M3+ HSS - High Speed Steel: M3+ HSS offers up to 100% longer tool life over M2-HSS. This super alloy steel is great for long runs or on tough hardwoods. M3+ HSS contains high levels of Vanadium, Tungsten, Molly, and Chromium for extended wear life. Treated to 66 Rc hardness which is one of the hardest HSS offered. Knife corrugations are 16 per inch at 60 degree angle.