Washer (mechanical) - AbsoluteAstronomy.com

A washer is a thin plate (typically disk-shaped) with a hole (typically in the middle) that is normally used to distribute the load of a threaded fastener

Threaded fastener

A threaded fastener is a discrete piece of hardware that has internal or external screw threads. They are usually used for the assembly of multiple parts and facilitate disassembly.The most common types are the screw and nut...

, such as a screw

Screw

A screw, or bolt, is a type of fastener characterized by a helical ridge, known as an external thread or just thread, wrapped around a cylinder. Some screw threads are designed to mate with a complementary thread, known as an internal thread, often in the form of a nut or an object that has the...

or nut

Nut (hardware)

A nut is a type of hardware fastener with a threaded hole. Nuts are almost always used opposite a mating bolt to fasten a stack of parts together. The two partners are kept together by a combination of their threads' friction, a slight stretch of the bolt, and compression of the parts...

. Other uses are as a spacer, spring (belleville washer

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 type of spring shaped like a washer. It has a frusto-conical shape which gives the washer a spring characteristic. The Belleville name comes from the inventor...

, wave washer), wear pad, preload indicating device, locking device, and to reduce vibration (rubber washer). Washers usually have an outer diameter

Diameter

In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints are on the circle. The diameters are the longest chords of the circle...

(OD) about twice the length of their inner diameter (ID).

Washers are usually metal

Metal

A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...

or plastic

Plastic

A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...

. High quality bolted joints require hardened steel washers to prevent the loss of pre-load due to Brinelling

Brinelling

Brinelling is a material surface failure caused by contact stress that exceeds the material limit. This failure is caused by just one application of a load great enough to exceed the material limit. The result is a permanent dent or "brinell" mark. It is a common cause of roller bearing failures,...

after the torque

Torque

Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....

is applied.

Rubber

Rubber

Natural rubber, also called India rubber or caoutchouc, is an elastomer that was originally derived from latex, a milky colloid produced by some plants. The plants would be ‘tapped’, that is, an incision made into the bark of the tree and the sticky, milk colored latex sap collected and refined...

or fiber

Fiber

Fiber is a class of materials that are continuous filaments or are in discrete elongated pieces, similar to lengths of thread.They are very important in the biology of both plants and animals, for holding tissues together....

gasket

Gasket

s used in taps

Tap (valve)

A tap is a valve controlling release of liquids or gas. In the British Isles and most of the Commonwealth, the word is used for any everyday type of valve, particularly the fittings that control water supply to bathtubs and sinks. In the U.S., the term "tap" is more often used for beer taps,...

(or faucets, or valves) to stop the flow of water 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.

Washers are also important for preventing galvanic corrosion, particularly by insulating steel screws from aluminum surfaces.

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.

Types

Washers can be categorised into three 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 loosening due to vibrations; and locking washers which prevent fastening loosening by preventing unscrewing rotation of the fastening device; locking washers are usually also spring washers. The term washer is also often used for disc shaped devices used as grommet

Grommet

thumb|right|250px|Some rubber grommets.A grommet is a ring inserted into a hole through thin material, such as fabric. Grommets are generally flared or collared on each side to keep them in place, and are often made of metal, plastic, or rubber. They may be used to prevent tearing or abrasion of...

Plain washers

A plain washer (or 'flat washer') is a flat annulus or ring

Annulus (mathematics)

In mathematics, an annulus is a ring-shaped geometric figure, or more generally, a term used to name a ring-shaped object. Or, it is the area between two concentric circles...

, often of metal, used to spread the load of a screwed fastening. Additionally a plain washer may be used when the hole is a larger diameter than the fixing nut.

A spherical washer is part of a self-aligning nut

Self-aligning nut

A self-aligning nut, also known as a spherical nut or leveling nut, is a type of nut that is used in applications where the fastener is not perpendicular to the surface the nut anchors to. It achieves this action by using a flanged nut inside a specially shaped dished out washer. They are commonly...

; it is a washer with one radiused surface, which is designed to be used in conjunction with a mating nut in order to correct for up to several degrees of misalignment between parts.

An anchor plate
Anchor plate
An anchor plate or wall washer is a large plate or washer connected to a tie rod or bolt. Anchor plates are used on exterior walls of masonry buildings, for structural reinforcement. Being visible, many anchor plates are made in a style that is decorative.One popular style is the star anchor—an...

or wall washer is a large plate or washer connected to a tie rod or bolt. Anchor plates are used on exterior walls of masonry buildings, for structural reinforcement. Being visible, many anchor plates are made in a style that is decorative.

A flange nut
Flange nut
A flange nut has a wide flange at one end that acts as an integrated, non-spinning washer. This serves to distribute the pressure of the nut over the part being secured, reducing the chance of damage to the part and making it less likely to loosen as a result of an uneven fastening surface.MATERIAL...

is a nut with an integral fixed washer.

A torque washer is used in woodworking

Woodworking

Woodworking is the process of building, making or carving something using wood.-History:Along with stone, mud, and animal parts, wood was one of the first materials worked by early humans. Microwear analysis of the Mousterian stone tools used by the Neanderthals show that many were used to work wood...

in combination with a carriage bolt; it has a square hole in the center where the carriage bolt square fits into. Teeth or prongs on the washer bite into the wood preventing the bolt from spinning freely when a nut is being tightened.

Spring and locking washers

Belleville washer
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 type of spring shaped like a washer. It has a frusto-conical shape which gives the washer a spring characteristic. The Belleville name comes from the inventor...

s, also known as a cupped spring washer or conical washer, has a slight conical shape, which provides an axial force when deformed.

Curved disc spring is similar to a Belleville except the washer is curved in only one direction, therefore there are only four points of contact. Unlike Belleville washers, they only exert light pressures.

Wave washers have a "wave" in the axial direction, which provides spring pressure when compressed. Wave washers, of comparable size, do not produce as much force as Belleville washers. In Germany, they are used as a lock washer, however they are ineffective.

A split washer is a ring split at one point and bent into a helical shape. This causes the washer to exert a spring force between the fastener's head and the substrate. Applicable standards are ASME B18.21.1, DIN

Din

DIN or Din or din can have several meanings:* A din is a loud noise.* Dīn, an Arabic term meaning "religion" or "way of life".* Din is one of the ten aspects of the Ein Sof in Kabbalah ....

127B, and United States Military Standard NASM 35338 (formerly MS 35338 and AN-935).

A toothed lock washer, also known as a serrated washer or star washer, has serrations that extend radially inward and/or outward to bite into the bearing surface

Bearing surface

A bearing surface is a mechanical engineering term that refers to the area of contact between two objects. It usually is used in reference to bolted joints and bearings, but can be applied to a wide variety of engineering applications....

. This type of washer is effective as a lock washer when used with a soft substrate, such as aluminum or plastic. There are four types: internal, external, combination, and countersunk. The internal style have the serrations along the inner diameter of the washer, which makes them more aesthetically pleasing. The external style have the serrations around the outer diameter, which provides better holding power, because of the greater surface area. The combination style has serrations about both diameters, for maximum holding power. The countersunk style is designed to be used with flat-head screws.

Gaskets

The term washer is often applied to various gasket types such as those used to seal the control valve in taps

Tap (valve)

. Crush washers are made of a soft metal such as aluminium or copper and are used to seal fluid or gas connections such as those found in an internal combustion engine.

A shoulder washer is a plain washer type with integral cylindrical sleeve; they are used to keep separate different metal types, and a seals. This term is also used for electrically insulating grommet

Grommet

Specialised types

A Keps nut
Keps nut
A Keps nut, also called a K-nut or washer nut, is a nut with an attached, free-spinning washer. It is used to make assembly more convenient. Common washer types are star-type lock washers, conical, and flat washers....

or K-lock nut is a nut with an integral free spinning washer, assembly is easier because the washer is captive.

A top hat washer is a shoulder washer type used in plumbing for tap fitting.

Materials

Common materials include steel

Steel

Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...

, stainless steel

Stainless steel

In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....

, and plastic

Plastic

. Hardened washers are steel washers that have been heat treated. Other materials include aluminum, aramid

Aramid

Aramid fibers are a class of heat-resistant and strong synthetic fibers. They are used in aerospace and military applications, for ballistic rated body armor fabric and ballistic composites, in bicycle tires, and as an asbestos substitute. The name is a portmanteau of "aromatic polyamide"...

s, bimetal

Bimetal

Bimetal refers to an object that is composed of two separate metals joined together. Instead of being a mixture of two or more metals, like alloys, bimetallic objects consist of layers of different metals...

s, bronze

Bronze

Bronze is a metal alloy consisting primarily of copper, usually with tin as the main additive. It is hard and brittle, and it was particularly significant in antiquity, so much so that the Bronze Age was named after the metal...

, brass

Brass

Brass is an alloy of copper and zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties.In comparison, bronze is principally an alloy of copper and tin...

, ceramic

Ceramic

A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...

s, copper

Copper

Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...

, felt

Felt

Felt is a non-woven cloth that is produced by matting, condensing and pressing woollen fibres. While some types of felt are very soft, some are tough enough to form construction materials. Felt can be of any colour, and made into any shape or size....

, fiber

Fiber

s, hastelloy

Hastelloy

Hastelloy is the registered trademark name of Haynes International, Inc. The trademark is applied as the prefix name of a range of twenty two different highly corrosion-resistant metal alloys loosely grouped by the metallurgical industry under the material term “superalloys” or “high-performance...

, iron

Iron

Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

, leather

Leather

Leather is a durable and flexible material created via the tanning of putrescible animal rawhide and skin, primarily cattlehide. It can be produced through different manufacturing processes, ranging from cottage industry to heavy industry.-Forms:...

, mica

Mica

The mica group of sheet silicate minerals includes several closely related materials having highly perfect basal cleavage. All are monoclinic, with a tendency towards pseudohexagonal crystals, and are similar in chemical composition...

, Inconel

Inconel

Inconel is a registered trademark of Special Metals Corporation that refers to a family of austenitic nickel-chromium-based superalloys. Inconel alloys are typically used in high temperature applications. It is often referred to in English as "Inco"...

, Monel

Monel

Monel is a trademark of Special Metals Corporation for a series of nickel alloys, primarily composed of nickel and copper, with some iron and other trace elements. Monel was created by David H. Browne, chief metallurgist for International Nickel Co...

, rubber

Rubber

, silicon bronze, zinc

Zinc

Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...

, and titanium

Titanium

Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color....

Standard metric flat washers sizes

Nominal screw sizes M (mm)		Screw pitch thread P (mm)		Internal (Inside) diameter hole d1 (mm)	External (Outside) diameter d2 (mm)	thickness H (mm)
1st choice	2nd choice	coarse	fine
1		0.25		1.1	3	0.3
1.2		0.25		1.3	3.5	0.3
	1.4	0.3		1.5	4	0.3
1.6		0.35		1.7	4	0.3
	1.7			1.8	4.5	0.3
	1.8	0.35
2		0.4		2.2	5	0.3
2.5		0.45		2.7	6	0.5
	2.6			2.8	7	0.5
3		0.5		3.2	7	0.5
	3.5	0.6		3.7	8	0.5
4		0.7		4.3	9	0.8
5		0.8		5.3	10	1
6		1	0.75	6.4	12	1.6
	7	1		7.4	14	1.6
8		1.25	1	8.4	16	1.6
10		1.5	1.25 or 1	10.5	20	2
12		1.75	1.5 or 1.25	13	24	2.5
	14	2	1.5	15	28	2.5
16		2	1.5	17	30	3
	18	2.5	2 or 1.5	19	34	3
20		2.5	2 or 1.5	21	37	3
	22	2.5	2 or 1.5	23	39	3
24		3	2	25	44	4
	27	3	2	28	50	4
30		3.5	2	31	56	4
	33	3.5	2	34	60	5
36		4	3	37	66	5
	39	4	3	40	72	6
42		4.5	3	43	78	7
	45	4.5	3	46	85	7
48		5	3	50	92	8
	52	5	4	54	98	8
56		5.5	4	58	105	9
	60	5.5	4	62	110	9
64		6	4	66	115	9
	68			70	120	10
72				74	125	10
	76			78	135	10
80				82	140	12
	85			87	145	12
90				93	160	12
	100			104	175	14

External links

Typical USA Flat Washer Dimensions USS, SAE, Fender, and NAS washer ID & OD (mm)
American National Standard (ANSI) Type B Plain Washers
SAE Flat Washers Type A Plain Washers
USS & SAE Combined Flat Washer Dimensions
Flat Washer Thickness Table Steel Gage Thicknesses, non-metric

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