This is an OEM replacement part and is sold individually.
Its purpose is to filter out dust and debris from contaminating the carburetor and engine.
When replacing the filter you can open the package in comes in and put a bit of two cycle oil in the bag and let it absorb into the filter. Then remove it from the bag and squeeze it with a paper towel to remove the excess oil.
This will aid the filter in filtering out the unwantables.