Abstract: An elongated, generally U-shaped in cross-section, retainer strip, of the type which includes longitudinally extending, resilient, confronting semi-walls extending inwardly and downwardly from the free ends of the legs to grip the edges of a fibrous filter mat, includes a pair of exterior flanges. One exterior flange extends in spaced, parallel relation to one of the walls of the retainer strip to mount the retainer strip on a planar portion of a filter frame without rivets or cement. The other exterior flange extends in spaced, parallel relation to another wall of the retainer strip to secure the edges of a conventional screen or mesh backing member eliminating sheet metal tabs.