A security thread is a security feature of many banknotes to protect against

counterfeit To counterfeit means to imitate something authentic, with the intent to steal, destroy, or replace the original, for use in illegal transactions, or otherwise to deceive individuals into believing that the fake is of equal or greater value tha ...

ing, consisting of a thin ribbon that is threaded through the note's

paper Paper is a thin sheet material produced by mechanically or chemically processing cellulose fibres derived from wood, Textile, rags, poaceae, grasses or other vegetable sources in water, draining the water through fine mesh leaving the fibre e ...

. Usually, the ribbon runs vertically, and is "woven" into the paper, so that it at some places emerges on the front side and at the remaining places at the rear side of the paper. Usually, it is made of

metal A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typi ...

foil, but sometimes of

plastic Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adaptab ...

. Often, it has some text or numbers (e.g., the denomination)

engraved Engraving is the practice of incising a design onto a hard, usually flat surface by cutting grooves into it with a burin. The result may be a decorated object in itself, as when silver, gold, steel, or glass are engraved, or may provide an in ...

. Threads are embedded within the paper fiber and can be completely invisible or have a star burst effect, where the thread appears to weave in and out of the paper when viewed from one side. However, when held up to the light, the thread will always appear as a solid line. Features can be built into the thread material e.g.,

microprinting Microprinting is the production of recognizable patterns or characters in a printed medium at a scale that requires magnification to read with the naked eye. To the unaided eye, the text may appear as a solid line. Attempts to reproduce by meth ...

on a transparent plastic thread or adding materials so they fluoresce under

ultraviolet light Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiati ...

. The thread is a difficult feature to counterfeit but some counterfeiters have been known to print a thin grey line or a thin line of varnish in the area of the thread. Security threads can also be used as an anti-counterfeiting device in

passport A passport is an official travel document issued by a government that contains a person's identity. A person with a passport can travel to and from foreign countries more easily and access consular assistance. A passport certifies the perso ...

s. They are generally made of plastic and contain microprinting.

References

Banknotes Money forgery Currency production National Security Agency {{Banknote-stub