Will fit in NATO 40mm threaded mask. Novelty use only. Core to be filled with activated charcoal. Core to be adjusted for airflow, set in place using “Colet” Filter mediums to be cut using template and held in place with “Filter Holder”. Seal “Top” and “Body” with electrical tape. Wrenches used for tight assembly/disassembly. Fits well with Shark NV500 foam Filters.