The NiSi 77mm Metal Stack Caps are a set of top and bottom durable metal caps to fit 77mm filters. Simply screw your filters together then screw the stack caps on the top and bottom. The NiSi 77mm Metal Stack Caps can be used with a minimum of 1 x 77mm filter and can be used to protect 20+ 77mm filters screwed together. The metal construction offers protection to filter surfaces and protects the filters from dust, scratches, and fingerprints while not in use. The Stack Caps enable a more organized, streamlined system for storing and carrying your circular filters.