Abstract: A filter retaining mechanism for retaining a filter and a pre-filter in relation to a filter aperture of a filter frame. A base clip retained by a proximal portion of a shank engages a flange of the frame, and a filter/pre-filter clip is retained by a distal portion of the shank. The filter/pre-filter clip has a proximal retaining formation that forms a distal retaining surface of a first reception area for retaining a filter and a proximal retaining surface of a second reception area for retaining a pre-filter and a distal retaining formation that forms a distal retaining surface of the second reception area. The filter/pre-filter clip is pivotable about a longitudinal axis between a first condition wherein the proximal and distal retaining formations retain the filter and the pre-filter and a second condition wherein the proximal and distal retaining formations face away from the filter aperture to release the filter and the pre-filter.