Good Filter Company expanded metal pre-filters are made of multiple layers of expanded aluminum and aluminum filter screen and are enclosed in a heavy duty aluminum frame. The expanded metal layers in this pre-filter are of different weights and different diamond sizes and the aluminum filter screen is sometimes flat and sometimes corrugated (depending upon the thickness of the frame). Although it is not as efficient as the bonded aluminum mesh filter, it is almost indestructible. The frame is mechanically closed for greater gripping power of the frame to the filter media and mechanical closing also removes any sharp edges, but also to enhance the holding power of the frame to the filter media in the corner areas. This gives the filter more rigidity and durability for longer life under heavy use. All frame edges are rounded so they won’t split like sharp edged frames do. The frame is riveted in one corner with an aluminum rivet, not a thin metal tab that breaks easily like other pre-filters. Because of the way it is constructed, this expanded metal pre-filter is of better quality and is more durable and efficient than the normal expanded metal pre-filters. This industrial grade expanded metal air filter can be used for a pre-filter, a primary air filter or a grease filter in applications where heavy use is the norm.