These filter frames are made of aluminium and are only compatible with the Cokin NX-Series 100mm filter-holder. They can each receive one rectangular graduated ND filter 100x150mm made by another manufacturer than Cokin in their empty location, provided that its thickness is exactly 2mm. The DUO Pack also includes one screwdriver to attach the filter in the frame, two spare screws and ten stickers to note the exact type of filter on the frame. The filters are not included.