The pre-filter acts as the initial screening device for Hakko fume extractors. Relatively large particles are removed from the air stream by a polyester filter, similar to those used in home air conditioners. Clean Air Replacements pre- filters have an arsenate (the capability to collect particles from the air) of 83%. Proper use and maintenance of the pre-filter can extend the service life of the main filter, so it is very important that they be checked at least once a week to see if they need replacement. 5/Pk. NOTE: Not affiliated with Hakko Corporation, all use and references of Hakko and Hakko model numbers are property of Hakko Corporation.