Meopta Opemus variable contrast filter holders

Filter holders for Meopta Opemus enlarger, or any other enlarger taking a ~7x7cm variable contrast or color correction filters. Filter holders are not strictly necessary for most enlargers where the filter is above the lens, but fingerprints on the gels bother me.

Assembly: Cut variable contrast/color correction filter gel to fit frame. Glue frame together to secure the filter gel in the frame (a single drop of cyanoacrylate glue on each corner should be adequate).
If your enlarger's filter