The TR-6800FC is a filter cover for use with the TR- 6820N filter. 3M recommends the use of the filter cover in order to help physically protect the TR-6820N from damage. It is also used to hold the TR-6600 Prefilter or TR-662 Spark Arrestor in place.The TR 6800FC is a filter cover for use with the TR 6820N filter. 3M recommends the use of the filter cover in order to help physically protect the TR 6820N from 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 worn or damaged. The filter cover may be cleaned and reused.