I am trying to identify two 11x14 film holders I recently purchased. They are in terrific condition, constructed of wood and painted black. The retaining tab "piece" is made of metal and is screwed to the holder with two flat slotted screws on either end of the "piece." The t-depth of the holders appears to be .355" +/- .005". I can find no identifying marks anywhere on the holders or the darkslides. Any help would be appreciated.