This is a chipper blade, which is installed on wood chippers and is used for cutting up pieces of wood into small chunks. Chipper blades need to be sharpened at least once a year or after about 25 hours of use. If the chipper blades aren't maintained, they will become dull and won't provide the required level of cutting power needed for wood chippers. If wood chips from the chipper are uneven, shredded, or rough, then sharpening or replacement may be needed. Make sure to take out the spark plug before the hopper is removed and connected to the tool. Next, remove the housing around the blades and the rotor assembly. The bolts around the blades can be taken off using an Allen wrench. Remove the blades, but be sure that work gloves are used to prevent injury. The replacement blade can be installed at this time. This is an OEM replacement chipper blade that can be used on wood chippers from Craftsman, MasterCut, Cub Cadet, Yard-Man, Yard Machines, and MTD. It's sold individually and comes directly from the manufacturer. The replacement will require an Allen wrench set, a wrench set, a socket set, and pliers.