Mower blades come in a variety of hardnesses, but the most common are 1055 and 5160. 1055 is a medium-carbon steel that is commonly used for making knives and swords. It has a Rockwell hardness of 56-58. 5160 is a high-carbon steel that is often used for springs and other applications where toughness is important. It has a Rockwell hardness of 61-63.