Ferrule

A ferrule (a corruption of Latin viriola "small bracelet," under the influence of ferrum "iron.") is a name for types of metal objects.

Most consist of a circular clamp used to hold together and attach fibers, wires or posts.

Examples of such ferrules:

In a brush the ferrule binds the bristles or hair to the handle.
The metal ring which is crimped to hold the eraser in place on pencils with an attached eraser.
The metal ring which holds a chisel blade's tang to the handle.
The metal cap put on the end of a bicycle's cable housing.
In fiber optic terminations, glass or plastic fibers are bonded to precision ferrules and polished for spliting or connecting two fibers together.
In restorative dentistry: margin of a cast crown that stabilizes root-canal treated teeth
In golf:plastic sleeve that adorns the bottom of most steel and graphite shafts just above the club head hosel. Originally designed to protect the shaft from damaging vibrations, it is now used mainly for aesthetic purposes.
Compression fittings for attaching tubing (piping) commonly have ferrules in them.

Not to be confused with a ferula, the Latin name of a plant, and of a punishment device used to hit a pupil on the palm of the hand or on the knuckles.