Fotasy 77mm Filter Stack Caps consists of a set of top and bottom durable metal caps to fit filters with different diameters. Simply screw your filters together then screw the stack caps on the top and bottom. They will protect the filters from dust, scratches and fingerprints while not in use. Additionally, these caps enable a more organized, streamlined system for storing and carrying your filters. Made of aluminum alloy, the filter cap is slim and exquisite. Easy to carry and takes up a little space.