Part # 9-0858-01 is an air filter replacement that simply covers the intake barb on the 9-1056-01 APG Ozone Module so that bugs, dust and debris don’t get lodged into your ozone system, causing failure.
Most of the time, you can re-use the air filter on your old APG Module(s), but it is recommended that you fully replace the air filter each time you change the APG Ozone Module (every 3-5 years).