This is a genuine replacement air filter designed for use with select models of lawn and garden trimmers. The air filter fits into a special assembly located near or on the carburetor and is designed to filter the air coming into the carburetor from the outside. The filter will remove debris and particles before allowing the air to pass into the engine, which means it will naturally become clogged with regular use over time. Air filters are typically a routine maintenance part and some owners will keep an extra filter on hand just in case they need it. When the filter is clogged, it will need to be replaced, whether it is time for maintenance or not. This genuine OEM air filter is manufactured by MTD and compatible with a number of trimmers from the brand, as well as select models from Yard Man, Cub Cadet, and Yard Machines. The air filter is made of durable foam material and designed to fit over the plastic air cleaner assembly, which is underneath the air cleaner cover. No tools are required to replace this part since the air cleaner cover snaps onto the base. This is sold as an individual unit and does not include the air filter assembly.