Washers

What are washers?

Washers are thin, flat or shaped discs with a hole in the centre, fitted under the head of a bolt or screw, or under a nut, to improve the way a fastener works. Depending on their design, washers spread the clamping load over a larger area, protect surfaces from damage, help prevent fasteners loosening, provide spacing, seal joints, or lock bearing nuts in place. Although they are small and simple, washers play an important part in making bolted joints and assemblies secure and reliable.

Washers are usually described by their inside diameter, outside diameter, and thickness, along with the bolt or shaft size they suit. Many are made to recognised DIN or ISO standards, which set their dimensions and make them interchangeable between suppliers.

The range covers several main groups:

• Flat washers - spread the load of a bolt or nut and protect the surface underneath
• Spring and locking washers - help resist loosening caused by vibration
• Bearing lock washers - tabbed washers used with bearing lock nuts to stop them turning on shafts and adapter sleeves
• Tab washers - folded against a nut or bolt head to lock it in position
• Sealing washers - seal threaded joints against leaks of oil, fuel, water, and air
• Spacer and shim washers - provide precise spacing or adjustment between parts

Key features:

• Load distribution - spreads clamping force over a wider area, reducing damage to soft or thin materials
• Surface protection - prevents nuts and bolt heads digging into or scratching the surface
• Anti-loosening - locking and tab washers help keep fasteners tight under vibration
• Sealing - sealing washers stop leaks at threaded connections
• Spacing and adjustment - spacer and shim washers set accurate gaps and positions
• Standardised sizes - many washers are made to DIN and ISO standards
• Range of materials and finishes - steel, stainless steel, brass, copper, nylon, and fibre, with plated and plain finishes

In simple terms, washers are the small components that help fasteners grip properly, stay tight, seal, and protect the parts they hold together.

Why are washers essential?

Washers are essential because bolted joints often need more than just a bolt and nut to work properly. Without a washer, a nut or bolt head can dig into soft materials, crush thin panels, or pull through oversized holes. Vibration can cause fasteners to loosen over time, and threaded joints in hydraulic, fuel, and oil systems can leak. Choosing the right washer helps prevent these problems and keeps assemblies safe and reliable.

Their main benefits are:

• Stronger joints - spreading the load helps maintain clamping force and prevents surface damage
• Protects materials - reduces damage to soft metals, plastics, wood, and painted surfaces
• Covers oversized holes - larger washers bridge slotted or oversized holes
• Helps prevent loosening - locking, tab, and bearing lock washers resist vibration
• Secures bearings - bearing lock washers keep lock nuts tight on shafts and sleeves
• Prevents leaks - sealing washers keep fluids and air inside the system
• Accurate spacing - spacer and shim washers set gaps, alignment, and end float
• Low cost - inexpensive components that protect more valuable parts

Washers are used across a wide range of industries and applications, including:

• Engineering and maintenance - general bolted joints on machinery and equipment
• Bearing installation - locking bearing nuts on shafts and adapter sleeves
• Construction and steelwork - structural fixings, frames, and brackets
• Automotive and transport - engine, chassis, brake, and fuel system fixings
• Hydraulic and pneumatic systems - sealing threaded ports and fittings
• Agricultural machinery - fixings on tractors, implements, and trailers
• Electrical installations - securing terminals and providing insulation
• Manufacturing and assembly - production lines and assembled products

The main types of washers

Washers are usually grouped by their shape, the job they do, and their material.

Flat washers:

• Standard flat washers - the most common type, spreading the load under bolts and nuts. Made to standards such as DIN 125 and ISO 7089
• Form A and Form B flat washers - Form A washers have plain edges, while Form B washers have one chamfered edge to sit neatly under bolt heads
• Large flat washers - also called repair or penny washers, these have a larger outside diameter to spread loads further and cover oversized holes. Made to standards such as DIN 9021 and ISO 7093
• Heavy-duty washers - thicker washers for structural and high-load applications

Spring and locking washers:

• Spring washers - split, slightly twisted washers that act as a spring under the nut or bolt head, helping to maintain tension. Made to standards such as DIN 127
• Toothed lock washers - have internal or external teeth that bite into the nut and surface to resist loosening. Made to standards such as DIN 6797
• Serrated lock washers - have fine serrations around the edge for grip on the surface. Made to standards such as DIN 6798
• Wave washers - curved washers that provide a light spring force, often used to take up end float in bearing assemblies
• Disc springs - conical washers that provide high spring force in a small space, used for preload and vibration control

Bearing lock washers:

• Bearing lock washers - also called tab washers or locking washers for bearings, these have an internal tab that fits into a keyway or slot on the shaft or adapter sleeve, and external tabs that bend into the slots of the bearing lock nut. This stops the lock nut turning and loosening
• Size designations - bearing lock washers are made in sizes to match their lock nuts, such as MB0, MB2, MB3, and MB7. The number usually matches the lock nut size and relates to the shaft diameter, such as MB0 for 10 mm, MB2 for 15 mm, MB3 for 17 mm, and MB7 for 35 mm

Tab washers:

• Tab washers with external tabs - tabs are bent up against the flat of a nut or bolt head and down over an edge to lock it in place. Made to standards such as DIN 93 and DIN 463

Sealing washers:

• Bonded seals - metal washers with a bonded rubber sealing ring, used to seal threaded ports in hydraulic and pneumatic systems
• Copper washers - soft metal washers that crush slightly to seal, used on fuel, oil, brake, and drain plug connections
• Fibre and nylon washers - used for sealing, insulation, and protecting surfaces

Spacer and shim washers:

• Shim washers - thin, precise washers used to adjust spacing and end float in assemblies. Made to standards such as DIN 988
• Spacer washers - thicker washers used to create set gaps between parts

By material:

• Steel - strong and economical, usually zinc plated for corrosion protection
• Stainless steel - corrosion resistant, usually A2 or A4 grades, ideal for outdoor, marine, and food environments
• Spring steel - used for spring washers, wave washers, and disc springs
• Brass and copper - corrosion resistant and used for sealing and electrical applications
• Nylon and fibre - lightweight, non-conductive, and gentle on surfaces

By finish:

• Bright zinc plated - a common finish with good corrosion protection for general use
• Self-colour - plain, uncoated steel, usually lightly oiled
• Hot dip galvanised - thick zinc coating for outdoor and structural use
• Stainless steel - naturally corrosion resistant, without a coating

How to choose the right washers?

Choosing the right washer means matching it to the fastener, the material, and the job it needs to do. Work through these points in order:

• Job type - decide whether you need to spread load, lock a fastener, lock a bearing nut, seal a joint, or set spacing
• Bolt or shaft size - choose a washer with an inside diameter that suits the bolt, screw, or shaft, such as M8, M10, or a 35 mm shaft
• Outside diameter - choose a standard washer for general use, or a large washer to spread load further or cover oversized holes
• Thickness - choose a thicker washer for heavy loads and a thinner washer where space is limited
• Standard - choose washers made to recognised DIN or ISO standards for consistent dimensions and interchangeability
• Locking method - for vibration, consider toothed, serrated, or tab washers, or other locking methods such as thread lockers or locking nuts for critical joints
• Bearing lock washers - match the washer to the bearing lock nut size and check the internal tab suits the keyway or slot in the shaft or sleeve
• Sealing - choose bonded seals, copper washers, or fibre washers to suit the fluid, pressure, and temperature
• Material - choose zinc plated steel for general use, stainless steel for corrosive environments, and nylon or fibre for insulation or surface protection
• Finish compatibility - match washers to the bolts and nuts, such as stainless washers with stainless fasteners and galvanised washers with galvanised fasteners
• Strength - for high-strength bolts, use hardened washers suitable for the bolt grade
• Quality and brand - choose washers from reputable suppliers for accurate dimensions and consistent quality

FAQ - All you need to know about washers

What does a washer do?

A washer spreads the load of a bolt or nut, protects the surface underneath, and can also help prevent loosening, seal joints, or provide spacing, depending on its type.

What is the difference between a flat washer and a spring washer?

A flat washer spreads the load and protects the surface. A spring washer is split and slightly twisted, acting as a spring under the nut or bolt head to help maintain tension.

Do spring washers stop bolts loosening?

They can help in some applications, but they are not always effective on high-strength or heavily loaded joints. For critical joints, consider other locking methods such as thread lockers, locking nuts, or tab washers.

What is a bearing lock washer?

A bearing lock washer is a tabbed washer used with a bearing lock nut. Its internal tab fits into a slot or keyway on the shaft or adapter sleeve, and one of its external tabs is bent into a slot on the lock nut to stop it turning.

What do MB numbers mean on bearing lock washers?

MB numbers show the size of the lock washer, which matches the lock nut size. For example, MB0 suits a 10 mm shaft, MB2 suits 15 mm, MB3 suits 17 mm, and MB7 suits 35 mm.

Can I reuse a bearing lock washer?

It is best to use a new lock washer each time. Bending the tabs weakens them, and a reused tab can crack or break.

What is a penny or repair washer?

A penny or repair washer is a large flat washer with a wide outside diameter. It spreads the load over a larger area and can cover oversized or damaged holes.

What is a bonded seal?

A bonded seal is a metal washer with a rubber sealing ring bonded to it, used to seal threaded ports in hydraulic and pneumatic systems.

Should I use a washer under the bolt head or the nut?

Usually under the part that is turned during tightening, which is often the nut. In some joints, washers are fitted under both the bolt head and the nut, especially on soft materials or oversized holes.

What material washer should I use?

Use zinc plated steel for general indoor use, stainless steel for outdoor or corrosive environments, hot dip galvanised washers with galvanised bolts, and nylon or fibre washers for insulation or protecting delicate surfaces.

Can I reuse washers?

Flat washers can often be reused if they are undamaged. Spring, tab, lock, sealing, and bearing lock washers should usually be replaced, as they may not lock or seal properly once used.