Compatibility and fit The Black Purification Elements are certified NSF/ANSI 42 and are compatible with Berkeyy Travel, Big, Royal, Imperial, Crown Series, Propur Traveler, Nomad, King, Big Series, Gravityy filter systems. They are designed to work with Doulton Super Sterasyl and ATC Super Sterasyl filters, W9361122 and W9361123 systems. The included washer and wingnut are accurately designed for a tight, leak fit. Safe materials Replacement filters are made of natural coconut shell activated carbon. Filter material is rigorously controlled, and the housing is produced with lead and BPA materials to ensure removal performance while preventing contaminants from leaking back into your water. Easy to carry Ideal for home, travel, outdoor activities, and emergencies such as water shortages. The filter provides healthy, clean, and quality water for both indoor and outdoor use. Longer service life To prolong the life of your appliance and achieve optimum performance, the filter every 6,000 gallons per pair; actual life may vary based on water conditions.