Ferrule

A ferrule (a corruption of Latin ' "small bracelet", under the influence of ' "iron") is any of a number of types of objects, generally used for fastening, joining, sealing, or reinforcement. They are often narrow circular rings made from metal, or less commonly, plastic. Ferrules are also often referred to as eyelets or grommets within the manufacturing industry.
Most ferrules consist of a circular clamp used to hold together and attach fibers, wires, or posts, generally by crimping, swaging, or otherwise deforming the ferrule to permanently tighten it onto the parts that it holds.
Reasons for use.
Some of the reasons people use ferrules include: