That is not a nut, depending on which type you have, if you look near the end, you should see a small slot. In that slot is what looks like a "flat wire". Turn the end of the cylinder until you find the end. Fish it out then turn the end and it will extract the wire (you should see one in your rebuild kit.). That wire fits in a grove that holds the end on. On some types you can just pull it out once you get it started.
Hope this helps,
Gary