Our V-FACE™ filter frames are designed for a standard depth 4″ filter of any efficiency with an optional prefilter link in front if desired. As is, with no additional changes to the frame, you may also use two of any variety of the standard size 2″ nominal depth filters installed back-to-back with a face mounted gasket in-between. Any 2″ prefilter, 2″ final (Now up to MERV 15), 2″ carbon (non-dusting options), can easily be provided. Contact us today with your requirements.