A spare fill port cap for JTS Airguns is a small plastic or metal cap that fits securely over the fill port on the airgun's reservoir. This cap is designed to prevent dirt, dust, and debris from entering the fill port when not in use, helping to maintain the airgun's performance and reliability over time. Spare fill port caps can be useful for airgun owners who frequently transport their airguns, as the caps can help prevent damage to the fill port during travel.