The TR-6500FC is a filter cover for use with the TR-6510N, TR-6530N and TR-6590N cartridges. 3M recommends the use of the filter cover in order to help protect cartridges from physical damage. The filter cover is also used to hold the TR-6600 Prefilter or TR-662 Spark Arrestor in place. The filter cover may be cleaned and reused, and should be replaced when worn or damaged.