This 3M filter cover is for use with TR-6820E filter on the TR619UK turbo unit. This cover is essential to protect the filter from physical damage and also to hold the TR-6600 prefilter or TR-662 spark arrestor in place. Can be cleaned and reused but it should be replaced when physically damaged. Filter cover for use with the TR-6820E filter. 3M recommends the use of the filter cover in order to help protect the TR-6820E from physical damage. It is also used to hold the TR-6600 Prefilter or TR-662 Spark Arrestor in place. The TR-6800FC should be replaced when damaged. The filter cover may be cleaned and reused.