The ferrule, the plastic, metal or ivory band around the end of the pool cue just below the cue tip, takes much of the pressure when the cue strikes a ball. For this reason cues used at the break are more prone to ferrule problems than cues used in other parts of the game. According to Royal Snooker.com, you should check the ferrule every time you replace the tip of the cue. If the ferrule is loose, you can glue it back in place or replace it. Some billiard players also replace ferrules that become discoloured from pool chalk.
Removing the old ferrule can be difficult if the glue holding the ferrule to the wood is solid. You can easily remove a loose ferrule in need of replacement. Use a lathe to cut away the ferrule if it is solidly attached to the cue. Be sure not to cut away any of the wood of the cue while removing the ferrule.
Sand away any remaining glue on the wood of the cue. Remove as little material as possible while still providing a smooth surface for the ferrule to slide onto the cue. If too much wood is removed, the ferrule will not fit solidly and could be difficult to keep straight with the body of the cue.
Replace the ferrule with one similar, if not identical, to the ferrule you removed. Ferrules, like cues, come in a variety of diameters. Changing the material or size of the ferrule can change the balance of the cue.
Glue the ferrule in place using super glue. Allow the ferrule to dry before sanding off any glue that may have oozed from the joints.
High end pool cues usually come with some spare parts when purchased new. The spare ferrule in these parts would be identical to the one originally installed on the cue and won't affect the balance of the cue. Replacing a pool cue ferrule can be difficult. It may be advisable to practice the procedures on an old pool cue rather than a prized stick.
Some antique cues have ivory ferrules. The value of a collector's item cue would likely be damaged if the ivory ferrule, even if it is discoloured, were replaced with plastic.