3M™ Versaflo™ Pre-filter, TR-6600 (Pack of 10)Pre filter can extend the service life of the particulate element of TR 600 series filters by capturing large particles that may otherwise clog the filter. Frequent pre filter changeout may help optimise system performance. The TR 6600 prefilter can extend the service life of the particulate (HE) element of TR 600 series filters and cartridges by capturing large particles that may otherwise clog the HE filter. Frequent prefilter changeout may help