This square key is a genuine MTD part, sold individually. This square key can be used as a replacement part in lawnmowers, snowblowers, tillers, leaf blowers, edgers, log splitters, and wood chippers. The purpose of the square key for one of these small engine outdoor appliances is to fit tightly into the gears, cams, sprockets, and pulleys within the general internal machinery of the appliances to keep the parts affixed to the shaft.The square key in a small engine outdoor appliance might have to be replaced if the square key is lost or misplaced, as it is a small component that can easily go missing without announcing its absence. The square key can also be damaged from general wear and tear over long-term use, meriting its replacement by this genuine OEM replacement part.This component is a genuine OEM replacement part sourced directly from the manufacturer. It is sold individually. This square key is compatible with the following outdoor appliance brands: MTD, Craftsman, Cub Cadet, Yard Machines, Huskee, Montgomery Wards, Yard-Man, Turf King, and MasterCut.