A ferrule is a connector that attaches the tap handle to the threaded rod (or pin rod) coming out of the tap. The ferrule can be either decorative or functional.

With a functional ferrule, it may be serving as a female to female connector between the threaded rod coming out of the main tap handle and the threaded rod from the tap. It may also be serving as an adapter between the threaded rod from the handle and the threaded rod from the tap.

When the ferrule is adapting the rod it’s normally adapting from a smaller thread size from the tap handle to the larger threaded rod for the tap.
A standard tap faucet will use 3/8 16 threading. Some tap handles will use the ferrule to connect a 3/8 hangar bolt or threaded rod from the handle to the 3/8 threaded rod from the tap faucet. Other tap handles will use 1/4 or 5/16 threading, in this case, the ferrule will be adapting the thread size and connecting the two male ends.

If you have a tap handle with a section of threaded rod or hangar bolt coming out of the end it is possible that the ferrule was removed. It is fairly easy to find a replacement ferrule. When you are getting a new ferrule, make sure you check the threading to make sure you get the right size.

Guinness Nitro taps typically connect to their tap faucets with a ferrule that uses a pin. If you are planning on using them on a tap or kegerator that doesn’t have the nitro draft you’ll want to see about getting an adaptor. Many of the adaptors that connect the Guinness Nitro ferrule to the 3/8 threading require the pin to be attached. Many times the taps will not come with the connector pin, if this is the case you can buy one separately.