M2-HSS - High Speed Steel: Our true grade M2-HSS (AISI) steel offers 25% longer run times than D2-HCHC grade. Our Premium M2-HSS offers high levels of Tungsten (6% W), Molybdenum (5.5% Mo), and Vanadium (2.2%V). M2-HSS is hardened to 63 Rc for better wear resistance in harder woods. Great for long runs in most soft and hardwoods. Knife corrugations are 16 per inch at 60 degree angle.