This Air Filter / Grease Filter is made of multiple layers of expanded aluminum and is enclosed in an aluminum frame. The expanded metal layers in this air filter / grease filter are of different weights and different diamond sizes, and although it is not as efficient as the bonded aluminum mesh filter, it is almost indestructable. The frame is hand closed for greater gripping power of the frame to the filter media and all corners are hammered to remove 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 and that corner is flattened so the rivet grips more firmly. Because of the way it is constructed, this air filter / grease filter is of better quality and is more durable and efficient than the normal 1/2" expanded metal filter. Although this air filter / grease filter is commonly listed as a 1/2" thick filter, the actual thickness is 3/8". This industrial grade air filter / grease filter can be used for a pre-filter, a primary air filter or a grease filter in applications where heavy use is the norm.