This air filter can be used as a replacement for the small engine of a leaf blower or a leaf vacuum. The function of an air filter is to prevent the engine from accumulating dust, debris, pebbles, and other small external materials picked up by the leaf blower or leaf vacuum in the process of operating the equipment.An air filter might have to be replaced if it suffers damage that prevents it from blocking external materials from entering the internal infrastructure of the appliance. An air filter that is damaged or needs replacement might clog with debris and prevent the engine from properly starting or might have tears and rips allowing dirt and debris to pass through the filter and cause internal damage to other components. If this is the case, the air filter must be immediately removed and replaced with this genuine OEM replacement part. Remember to always wear gloves when handling, repairing, and operating outdoor equipment. This is an OEM part sourced directly from the manufacturer, MTD. It is sold individually. This air filter is compatible with the following brands: MTD, Troy-Bilt, and Craftsman.