Lower cost filter frames are fabricated out of galvanized steel and are left bare. Both sides of the frame use hardware cloth to retain the filter media. An insert of bulk, polyester filter material or a cardboard filter serves as the air filtration medium.

The upstream side of the filter frame fits over the other half of the frame like a clamshell and is supplied with two clamping pads to allow it to be clamped into the air duct. One inch square tube can be used for the clamping pad to allow a 1" thick filter frame to be clamped in the duct where a 2" filter formerly was used.