ferrule

A ferrule is a ring, cap, or crown, typically made of metal, that encircles and reinforces the end of a component or joins two parts. It is commonly found on hand tools, brushes, broom handles, and some musical instruments, serving to hold parts together and distribute stress.

In hand tools, ferrules are fitted around the end of a wooden handle to secure the tool head, such as axes, hammers, saws, and chisels. They help transfer impact forces, prevent the handle from splitting, and resist shear. In brushes and brooms, the ferrule is the metal ring that binds the bristles or fibers to the handle. In furniture and some musical instruments, ferrules can provide both decorative appeal and a structural role by binding components at joints or transitions.

Materials and manufacturing methods vary. Ferrules are typically made from steel (carbon or stainless), aluminum, brass, or nickel-silver, and may feature protective coatings or finishes. They are usually installed by swaging, crimping, or press-fitting around the substrate; in wood-handled tools, they may be secured with adhesive or pins in addition to crimping.

Dental ferrule refers to a band of tooth structure that surrounds the externally prepared tooth crown, contributing to the retention and fracture resistance of a crown. The ferrule effect emphasizes preserving sufficient coronal tooth structure, with guidelines often citing a minimum of about 1.5 to 2 millimeters.

Etymology traces the term to French ferrure, from Latin ferrum meaning iron, reflecting the metal ring’s fundamental nature.