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A washer is a thin plate (typically disk-shaped, but sometimes square) with a hole (typically in the middle) that is normally used to distribute the load of a
threaded fastener shown for scale) A fastener (US English) or fastening (UK English) is a Household hardware, hardware device that mechanically joins or affixes two or more objects together. In general, fasteners are used to create non-permanent joints; that is, j ...
, such as a
bolt Bolt or bolts may refer to: Implements and technology * Bolt (fastener) A bolt is a form of threaded fastener with an external male thread requiring a matching pre-formed female thread such as a nut. Bolts are very closely related to screw ...
or
nut Nut often refers to: * Nut (fruit), a fruit composed of a hard shell and a seed * Nut (food), collective noun for dry and edible fruits or seeds * Nut (hardware), a fastener used with a bolt Nut or Nuts may also refer to: Places * Nomenclature of ...
. Other uses are as a spacer, spring (
Belleville washer A Belleville washer, also known as a coned-disc spring, conical spring washer, disc spring, Belleville spring or cupped spring washer, is a conical shell which can be loaded along its axis either statically or dynamically. A Belleville washer is ...

Belleville washer
, wave washer), wear pad, preload indicating device, locking device, and to reduce vibration (
rubber washer Image:Rubber washer.jpg, right A rubber washer is a ring made of rubber used in mechanical devices. It is used to prevent vibration from spreading from one part to another, reducing the noise levels. Typical uses are mounting computer parts, like F ...

rubber washer
). Washers are usually
metal A metal (from Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10.7 mi ...

metal
or
plastic Plastics are a wide range of synthetic polymers, synthetic or semi-synthetic materials that use polymers as a main ingredient. Their Plasticity (physics), plasticity makes it possible for plastics to be Injection moulding, moulded, Extrusion, ext ...

plastic
. High-quality
bolted joint, right Bolted joints are one of the most common elements in construction and machine design. They consist of fasteners that capture and join other parts, and are secured with the mating of screw threads. There are two main types of bolted join ...

bolted joint
s require hardened steel washers to prevent the loss of pre-load due to
brinelling Brinelling {{IPAc-en, ˈ, b, r, ɪ, n, ə, l, ɪ, ŋ is the permanent indentation hardness, indentation of a hard surface. It is named after the Brinell scale of hardness, in which a small ball is pushed against a hard surface at a preset level of f ...
after the
torque In physics and mechanics, torque is the rotational equivalent of linear force In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the na ...

torque
is applied. Washers are also important for preventing
galvanic corrosion Galvanic corrosion (also called bimetallic corrosion or dissimilar metal corrosion) is an electrochemical Electrochemistry is the branch of physical chemistry concerned with the relationship between electrical potential, as a measurable and quant ...
, particularly by insulating steel screws from aluminium surfaces. They may also be used in rotating applications, as a bearing. A ''thrust washer'' is used when a
rolling element bearing A rolling-element bearing, also known as a rolling bearing, is a bearing (mechanical), bearing which carries a load by placing rolling elements (such as balls or rollers) between two bearing rings called Race (bearing), races. The relative motion o ...
is not needed either from a cost-performance perspective or due to space restraints.
Coating A coating is a covering that is applied to the surface of an object, usually referred to as the substrate Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium ...
s can be used to reduce wear and friction, either by hardening the surface or by providing a solid lubricant (i.e. a self-lubricating surface). The origin of the word is unknown; the first recorded use of the word was in 1346, however, the first time its definition was recorded was in 1611.
Rubber Rubber, also called India rubber, latex, Amazonian rubber, ''caucho'', or ''caoutchouc'', as initially produced, consists of polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, ...

Rubber
or
fiber Fiber or fibre (from la, fibra, links=no) is a natural Nature, in the broadest sense, is the natural, physical, material world or universe The universe ( la, universus) is all of space and time and their contents, including ...
gasket Some seals and gaskets A gasket is a Seal (mechanical), mechanical seal which fills the space between two or more mating surfaces, generally to prevent leakage from or into the joined objects while under compression (physical), compression. Giv ...

gasket
s used in
taps "Taps" is a bugle call plays the bugle during the Gulf War, in March 1991. A bugle call is a short melody, tune, originating as a military Military communications, signal announcing scheduled and certain non-scheduled events on a military inst ...
(or faucets, or valves) as seal against water leaks are sometimes referred to colloquially as ''washers''; but, while they may look similar, washers and gaskets are usually designed for different functions and made differently.


Washer types

Most washers can be categorized into three broad types; * ''Plain washers'', which spread a load, and prevent damage to the surface being fixed, or provide some sort of insulation such as electrical * ''Spring washers'', which have axial flexibility and are used to prevent fastening or loosening due to vibrations * ''Locking washers'', which prevent fastening or loosening by preventing unscrewing rotation of the fastening device; locking washers are usually also spring washers.


Plain washers


Spring and locking washers

Lock washers,
locknut A locknut, also known as a lock nut, locking nut, self-locking nut, prevailing torque nut,. stiff nut or elastic stop nut, is a Nut (hardware), nut that resists loosening under vibrations and torque. Elastic stop nuts and prevailing torque nuts ar ...
s,
jam nut A jam nut is a low profile type of nut, typically half as tall as a standard nut. It is commonly used as a type of locknut, where it is "jammed" up against a standard nut to lock the two in place. It is also used in situations where a standard nut ...
s, and
thread-locking fluid Bolts with thread-locking fluid applied Thread-locking fluid or threadlocker is a thin, single-component adhesive adhesive dispensed from a tube Adhesive, also known as glue, cement, mucilage, or paste, is any non-metallic substance applied t ...

thread-locking fluid
are ways to prevent vibration from loosening a
bolted joint, right Bolted joints are one of the most common elements in construction and machine design. They consist of fasteners that capture and join other parts, and are secured with the mating of screw threads. There are two main types of bolted join ...

bolted joint
.


Gaskets

The term washer is often applied to various gasket types such as those used to seal the control valve in
taps "Taps" is a bugle call plays the bugle during the Gulf War, in March 1991. A bugle call is a short melody, tune, originating as a military Military communications, signal announcing scheduled and certain non-scheduled events on a military inst ...
.


Specialised types

The DIN 125 metric washer standard refers to subtypes A and B. ISO 7089 calls these Form A and ISO 7090 calls them Form B. They are all the same overall size, but Form B is chamfered on one side.


Materials

Washers can be fabricated from a variety of materials including, but not limited to: *
Steel Steel is an alloy An alloy is an admixture of metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appea ...

Steel
Carbon steel Carbon steel is a steel Steel is an alloy An alloy is an admixture of metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fract ...
,
spring steel Spring steel is a name given to a wide range of steel Steel is an alloy of iron with typically a few tenths of a percent of carbon to improve its strength of materials, strength and fracture toughness, fracture resistance compared to iron. Ma ...
, A2 (304) stainless steel, and A4 (316/316L) stainless steel *
Non-ferrous metal In metallurgy Metallurgy is a domain of Materials science, materials science and engineering that studies the physical and chemical behavior of metallic Chemical element, elements, their Inter-metallic alloy, inter-metallic compounds, and their ...
Copper Copper is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same nu ...

Copper
,
brass Brass is an alloy An alloy is an admixture of metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appear ...

brass
,
aluminium Aluminium (aluminum in and ) is a with the  Al and  13. Aluminium has a density lower than those of other common , at approximately one third that of . It has a great affinity towards , and of on the surface when exposed to air ...

aluminium
,
titanium Titanium is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same n ...

titanium
,
iron Iron () is a with Fe (from la, ) and 26. It is a that belongs to the and of the . It is, on , right in front of (32.1% and 30.1%, respectively), forming much of Earth's and . It is the fourth most common . In its metallic state, iron ...

iron
,
bronze Bronze is an alloy consisting primarily of copper, commonly with about 12–12.5% tin and often with the addition of other metals (such as aluminum, manganese, nickel or zinc) and sometimes non-metals or metalloids such as arsenic, phosphorus or ...

bronze
, and
zinc Zinc is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same numbe ...

zinc
*
Alloy An alloy is an admixture of metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts Elec ...
Silicon bronze,
Inconel Inconel is a registered trademark of Special Metals Corporation for a family of austenitic nickel-chromium-based superalloys. Inconel alloys are oxidation-corrosion resistance, corrosion-resistant materials well suited for service in extreme envi ...
,
Monel Monel is a group of nickel alloy An alloy is an admixture of metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lu ...
, and Hastelloy *
Plastic Plastics are a wide range of synthetic polymers, synthetic or semi-synthetic materials that use polymers as a main ingredient. Their Plasticity (physics), plasticity makes it possible for plastics to be Injection moulding, moulded, Extrusion, ext ...

Plastic
Thermoplastic A thermoplastic, or thermosoft plastic, is a plastic polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules, or macromolecules, ...
s and
thermosetting polymer In materials science, a thermosetting polymer, often called a thermoset, is a polymer that is obtained by Reversible process (thermodynamics), irreversibly hardening ("curing (chemistry), curing") a soft solid or viscous liquid prepolymer (resin). ...
s such as
polyethylene Polyethylene or (incorrectly) polythene (abbreviated PE; IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations that represents chemists in individual countr ...

polyethylene
,
PTFE Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene that has numerous applications. The commonly known brand name of PTFE-based compositions is Teflon by Chemours, a corporate spin-off, spin-off from DuPont (1802 ...

PTFE
(Teflon) *
Nylon Nylon is a generic designation for a family of s composed of s ( linked by links).The polyamides may be or . Nylon is a -like , generally made from , that can be melt-processed into fibers, , or shapes. Nylon polymers can be mixed with a w ...

Nylon
Nylon 6 molecule used to synthesize Nylon 6 by ring opening polymerization Nylon 6 or polycaprolactam is a polymer developed by Paul Schlack at IG Farben to reproduce the properties of Nylon 6-6, nylon 6,6 without violating the patent on its production. ...

Nylon 6
,
Nylon 66 Nylon 66 (loosely written nylon 6-6, nylon 6/6, nylon 6,6, or nylon 6:6) is a type of polyamideA polyamide is a polymer with repeating units linked by amide bonds. Polyamides occur both naturally and artificially. Examples of naturally occurrin ...

Nylon 66
, Nylatron, and Tecamid MDS * Specialty –
Fiber Fiber or fibre (from la, fibra, links=no) is a natural Nature, in the broadest sense, is the natural, physical, material world or universe The universe ( la, universus) is all of space and time and their contents, including ...

Fiber
s,
ceramic A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant Corrosion is a natural process that converts a refined metal into a more chemically stable form such as oxide of rutile. Ti(IV) centers are grey; oxygen ce ...

ceramic
s,
rubber Rubber, also called India rubber, latex, Amazonian rubber, ''caucho'', or ''caoutchouc'', as initially produced, consists of polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, ...

rubber
,
felt Felt is a textile material that is produced by matting, condensing and pressing fibers together. Felt can be made of natural fibers such as wool Wool is the textile fiber obtained from sheep and other animals, including Cashmere wool, ca ...
,
leather Leather is a strong, flexible and durable material obtained from the tanning Tanning may refer to: *Tanning (leather), treating animal skins to produce leather *Sun tanning, using the sun to darken pale skin **Indoor tanning, the use of arti ...

leather
, bimetals, and
mica Micas ( ) are a group of minerals whose outstanding physical characteristic is that individual mica crystals can easily be split into extremely thin elastic plates. This characteristic is described as perfect Cleavage (crystal), basal cleavage ...

mica
* Phenolic – The material has good electrical insulation, is lightweight, tough, has low moisture absorption, is heat resistant, and is resistant to chemicals and corrosion. Phenolic washers are substitutes for flat metallic washers in cases where electrical insulation is required. Phenolic washers are stamped out of large sheets of the phenolic material. The term “phenolic washer” is sometimes used for stamped washers from laminated materials such as paper, canvas, and
Mylar Metallized boPET film, 32 layers of ~14 µm thickness each BoPET (biaxially-oriented polyethylene terephthalate) is a polyester Polyester is a category of polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, - ...
.


Corrosion resistance

A number of techniques are used to enhance the
corrosion Corrosion is a that converts a refined metal into a more chemically stable form such as , , or . It is the gradual destruction of materials (usually a ) by chemical and/or electrochemical reaction with their environment. is the field dedica ...

corrosion
resistant properties of certain washer materials: * Metallic coatings – Typical coatings used to produce corrosion resistant washers are zinc,
cadmium Cadmium is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same nu ...

cadmium
, and nickel. Zinc coating acts as a sacrificial surface layer that falls victim to corrosive materials before the washer's material can be harmed. Cadmium produces a high-quality protective surface but is toxic, both biologically and environmentally. Nickel coatings add protection from corrosion only when the finish is dense and non-porous. *
Electroplating Electroplating is a general name for processes that produce a metal coating on a solid substrate through the redox, reduction of cations of that metal by means of a direct current, direct electric current. The part to be coated acts as the cathode ...
– This method involves coating the washer by electrolytic deposition using metals such as
chromium Chromium is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same nu ...

chromium
or
silver Silver is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same n ...

silver
. * Phosphating – A resilient, but
abrasive An abrasive is a material, often a mineral, that is used to shape or finish a workpiece through rubbing which leads to part of the workpiece being worn away by friction. While finishing a material often means polishing it to gain a smooth, reflect ...
surface is achieved by incorporating a zinc-phosphate layer and corrosion-protective oil. * Browning or bluing – Exposing the washer (typically steel) to a chemical compound or
alkali In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds composed of ato ...

alkali
salt solution causes an
oxidizing (mild reducing agent) are added to powdered potassium permanganate Potassium permanganate is an inorganic compound with the chemical formula KMnO4 and composed of potassium ion, K+ and permanganate, . It is a purplish-black crystalline salt, th ...

oxidizing
chemical reaction, which results in the creation of a corrosion-resistant, colored surface. The integrity of the coating can be improved by treating the finished product with a water-displacing oil. * Chemical plating – This technique utilizes a nickel-phosphor alloy that is precipitated onto the washer surface, creating an extremely corrosion- and abrasive-resistant surface.


Type and form

The
American National Standards Institute The American National Standards Institute (ANSI ) is a private non-profit organization A nonprofit organization (NPO), also known as a non-business entity, not-for-profit organization, or nonprofit institution, is a legal entity organized ...
(ANSI) provides standards for general use flat washers. Type A is a series of steel washers at broad tolerances, where precision is not critical. Type B is a series of flat washers with tighter tolerances where outside diameters are categorized as "narrow", "regular" or "wide" for specific bolt sizes. "Type" is not to be confused with "form" (but often is). The
British Standard British Standards (BS) are the standards produced by the BSI Group which is incorporated under a royal charter (and which is formally designated as the Standards organization#National standards bodies, national standards body (NSB) for the UK). The ...
for Metric Series Metal Washers (BS4320), written in 1968, coined the term "form". The forms go from A to G and dictate the outside diameter and thickness of the flat washers. * Form A: Normal diameter, normal thickness * Form B: Normal diameter, light thickness * Form C: Large diameter, normal thickness * Form D: Large diameter, light thickness * Form E: Normal diameter, normal thickness * Form F: Large diameter, normal thickness * Form G: Largest diameter, larger thickness.
Washer 'form' when comparing different washer material types is used quite freely by stockists. In relation to BS4320 specifically, washer forms 'A' to 'D' inclusive are designated ‘bright metal’ washers and are supplied self-finished in various metals including: steel alloys, brass, copper, etc. Whereas, BS4320 washer forms ‘E’ to ‘G’ inclusive are designated ‘black’ (uncoated) mild steel washers, which normally are specified with a supplementary protective coating supply condition.


Standard metric flat washers sizes

Washers of standard metric sizes equivalent to BS4320 Form A are listed in the table below. Measurements in the table refer to the dimensions of the washers as described by the drawing. Specifications for standard metric flat washers were known as DIN 125 (withdrawn) and replaced with ISO 7089. DIN (Deutsches Institut für Normung - German Institute for Standardization) standards are issued for a variety of components including industrial fasteners as Metric DIN 125 Flat Washers. The DIN standards remain common in Germany, Europe and globally even though the transition to ISO standards is taking place. DIN standards continue to be used for parts which do not have ISO equivalents or for which there is no need for standardization.


See also

* Bit guard *
Dowel A dowel is a cylindrical wikt:rod, rod, usually made of wood, plastic, or metal. In its original manufactured form, a dowel is called a ''dowel rod''. Dowel rods are often cut into short lengths called dowel pins. Dowels are commonly used as struc ...
*
Unified Thread Standard The Unified Thread Standard (UTS) defines a standard thread form and series—along with allowances, tolerances, and designations—for screw thread A screw thread, often shortened to thread, is a helix, helical structure used to convert between r ...


Notes


References

*


Further reading

* Parmley, Robert. (2000). "Section 11: Washers." ''Illustrated Sourcebook of Mechanical Components.'' New York: McGraw Hill. Drawings, designs and discussion of various uses of washers.


External links

*(http://www.fastenerdata.co.uk/flat-washers Dimensions of Global washers
ASME Plain washer dimensions (Type A and Type B)


USS, SAE, Fender, and NAS washer ID & OD (mm)



Type A Plain Washers


Flat Washer Thickness Table
Steel Gage Thicknesses, non-metric
Split Lockwashers: Truth vs. Myth
Hill Country Engineering
Using machine washers
Machine Design - Using washers {{Authority control Hardware (mechanical) Springs (mechanical) Ironmongery