A ferrule (a corruption of Latin viriola "small bracelet", under the influence of ferrum "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.
The plastic sleeve preventing the ends of shoelaces from unraveling (called the aglet)
The metal sleeve which is crimped to hold the eraser in place on pencils
The metal band that binds the bristles or hair of a brush to its handle
The metal ring which holds a chisel blade's tang to the handle
In fiber optic terminations, glass or plastic fibers are bonded to precision ferrule connectors (FCs), also described as fiber channel connectors, and polished for splitting or connecting two fibers together
The metal spike at the end of the shaft of an ice axe
The margin of a cast crown that stabilizes root-canal treated teeth in restorative dentistry
The bottom end of a flag stick on a golf course, which fits snugly into a hole in the cup
The plastic sleeve that adorns the bottom of most steel and graphite golf club shafts just above the club head hosel. Originally designed to protect the shaft from damaging vibrations, it is now used mainly for aesthetic purposes
The metal band used to prevent the ends of wooden instruments from splitting
The semi-circular metal band that holds the fibers in place on the frogs of bows for violin family instruments
Compression fittings for attaching tubing (piping) commonly have ferrules in them.
A swaged termination type for wire rope
The cap at the end of a cane or umbrella as well as the ring, often crimped, sometimes pinned, that prevents an umbrella's canopy from sliding off the end when open.
The portion of a cue in pool, billiards and snooker that tops the shaft and to which the tip is bonded; historically made of ivory, now typically made of fiberglass, phenolic resin or brass
The male and female joints that join one section of a two-piece fishing rod
A metal cap at the end of cable housing with a hole on bicycle or motorcycle control cables
The metal sleeve that connects a hypodermic needle to a plastic Luer taper (which then connects to a syringe or intravenous therapy tubing.)
A metal tube crimped over stranded wire to secure it within a screw terminal usually with electrical insulation protecting any exposed portion of the wire not completely inside the screw terminal post.
A metal or plastic ring used in plumbing as part of a compression fitting along with a slip-on nut for making a liquid-tight connection when joining pipe or tubing. (These are informally called "olives" in the U.K.)
Some of the reasons people use ferrules include:To shield parts or cables from electromagnetic pulses, environmental damage, the elements, thermal factors, and more.
To cover parts, adding wear resistance, damage protection, or packaging.
As a connector, to connect wires, structural devices, and systems
To bind parts together, including bundles of wires, or cloth threads to the end of the mop, as an example.
To act as conveyance for fluids like oil and water, or for gasses like air.