Washers

The Ultimate UK Guide to Washers: Where to Buy M8, M10 and More (in Inches)

Why the right washer really matters

If you’ve ever tightened a bolt only to find it pulls through soft material or loosens after a week, you know how a tiny washer can make or break a job. Washers distribute load, protect surfaces, prevent pull-through, and stop fasteners from loosening. Whether you’re hanging a shelf, wiring a junction box, or assembling garden furniture, picking the correct washer is like choosing the right pair of shoes for a hike—get it wrong and you’ll regret it halfway up the trail.

Types of washers and what they do

Washers come in more shapes than you’d expect. Each type solves a particular problem, and knowing the differences saves you time, money, and frustration on the workbench.

Flat washers

Flat washers are the most common. They sit under a nut or bolt head and spread the load across a broader area to protect the surface and reduce the chance of the fastener digging in. Think of them as a shock absorber in a little metal disc.

Mudguard (cup) washers

Mudguard washers, sometimes called cup washers, provide a neat finished look and allow the bolt head to sit flush or slightly recessed. They’re great for panels and trim where appearance matters, or where you want a tidier finish around a countersunk screw.

Square washers

Square washers are useful when working with timber or soft materials where the larger corner-to-corner contact avoids rotation and provides a wider bearing surface. They’re common in rustic or DIY carpentry jobs.

Specialist washers — spring and lock types

Lock and spring washers prevent loosening under vibration. They bite into the nut and the surface to keep the assembly tight. Use them in mechanical applications, engines, and anything that shakes or moves.

Materials and finishes: picking for durability

The material of a washer changes its job entirely. Steel is strong and affordable, brass looks great and resists corrosion in electrical use, and zinc or BZP (bright zinc plated) finishes add corrosion protection. If you’re working outdoors or near water, prioritize corrosion resistance.

Steel (plain and plated)

Plain steel is cheap and strong but will rust. Zinc-plated (BZP) steel adds a sacrificial layer to slow corrosion, making it a common choice for general-purpose jobs.

Brass

Brass washers are non-magnetic and conduct electricity, so they’re often used in electrical connections where you need a reliable, corrosion-resistant contact. They also add a neat, golden finish where appearance matters.

Stainless steel

Stainless is the top choice for long-term outdoor durability. It’s more expensive but resists rust like a champ, ideal for marine or exposed garden applications.

Common washer sizes explained (in inches)

UK stock lists often use metric sizes like M8 or M10, but if you prefer imperial units, here are handy equivalents so you can pick the right washer without a calculator. For most DIY work, you’ll see washers that match these bolt diameters:

- 5/16 inch (roughly equivalent to M8) — a common size for light structural and electrical work.

- 3/8 inch (roughly equivalent to M10) — used for heavier fixings and moderate structural loads.

- 15/32 inch (roughly equivalent to M12) — for heavier duty connections where strength matters.

Stores to buy washers in the UK

Whether you want a single decorative washer or a box of one hundred for a trade job, UK retailers stock a vast range. Below I run through the best high-street and online choices, what to expect from each, and where to find the specific types mentioned earlier.

Expert Electrical

Expert Electrical is a specialist supplier that carries a focused range of electrical hardware, including mudguard and flat washers ideal for wiring and panel work. Products you’ll commonly find there include Unitrunk mudguard washers in 5/16 inch and larger, Unitrunk flat washers around 5/16 inch, Unicrimp brass washer packs (great for electrical terminals), and CK branded washer boxes for regular trade users. If you’re wiring or doing electrical panel assemblies, this kind of specialist stock is worth checking first.

Screwfix

Screwfix is a go-to for many UK tradespeople and DIYers thanks to widespread stores and quick online ordering. They stock a broad mix—flat washers, spring washers, and plated sets in common sizes like 5/16 inch and 3/8 inch, in pack sizes from a few to hundreds. Screwfix is handy if you want same-day pickup from a local depot.

Toolstation

Toolstation mirrors Screwfix for convenience but often has different pack sizes and occasional offers. Look here for trade packs and branded hardware, plus clear product specs to help you match washers to bolts and screws.

Wickes and B&Q

Both Wickes and B&Q are excellent for household projects. Their stores stock common flat and spring washers in sizes suitable for furniture assembly, fencing, and garden hardware. They’re great when you need a few bits quickly and prefer in-person browsing.

RS Components

If you need technical specs and a large catalogue of specialist washers—like insulated electrical washers or precision thin washers—RS Components is worth a visit. They cater for industrial and professional needs, with items available in small or bulk quantities.

Amazon UK and eBay

Online marketplaces offer unbeatable variety and often the best prices on bulk packs. You’ll find branded packs like Unicrimp or CK in multiple quantities, but check seller reviews carefully and ensure the size is listed in inches or clearly convertible if you prefer imperial units.

Spotlight on popular products you’ll see

Some washer SKUs appear time and again on UK supplier lists. Here’s a plain-English description of the parts you’ll likely encounter at electrical suppliers and trade counters.

Unitrunk mudguard washer — 5/16 inch

This mudguard (cup) washer gives a neat recess for bolt heads and is popular for electrical trunking and panel trims. It hides the fastener head and spreads load—handy when working with thin sheet materials.

Unitrunk flat washer — 5/16 inch

A straightforward, dependable disc that distributes load under bolt heads. Use it under nuts in joinery or behind panel fixings to prevent pull-through.

Unicrimp brass washer pack of 100 — 5/16 inch

Brass washer packs are perfect for electrical terminals and decorative work. A box of 100 is a staple for electricians and hobbyists who need many small conductive washers for connections.

CK washer 5/16 inch pack of 100

CK is another brand often stocked by electrical retailers. A 100-pack keeps spares on hand for installation work and reduces downtime when you need replacements mid-job.

Unitrunk mudguard washers in 3/8 and 15/32 inch

For larger fixings, Unitrunk’s larger mudguard washers maintain that clean finish on heavier panels. Pick up these sizes when your bolts are 3/8 inch or larger and you need that recessed look and secure bearing.

Unicrimp 3/8 inch flat BZP pack of 10

For smaller projects where you don’t need a giant box, a pack of ten plated flat washers does the trick—good for repair jobs or finishing touch work.

Unitrunk square washer — 5/16 inch

Square washers are handy with timber or custom fixings where rotation restraint matters. They give extra bite at the corners and a bigger footprint than a round washer of the same diameter.

How to measure washers and match them to bolts

Matching washers to bolts is simple if you follow a couple of rules. Measure the bolt shank diameter (not the thread peaks) and choose a washer with an inner hole slightly larger than that diameter. For a 5/16 inch bolt, pick a washer with a 5/16 inch hole; for a 3/8 inch bolt, pick a 3/8 inch hole. If you’re in doubt, a slightly larger inner hole is okay; too tight and the washer won’t slide on.

Using calipers and drill bits

If you’re unsure, use calipers to measure bolts or test a washer hole against a known drill bit size. Drill bit sets are often labelled in inches and can be used as a quick gauge.

Smart buying tips to save money and avoid waste

Here are some practical pointers that help whether you’re buying one washer or a trade crate.

Buy pack sizes that match your needs

If you’ll be doing multiple projects, buying packs of 100 can be cheaper per unit. For a single household job, a pack of ten or a mixed assortment may be more sensible.

Think ahead with material choice

Don’t skimp on corrosion resistance for outdoor jobs. Spending a little more on stainless or plated washers now saves you from rusted fasteners later.

Look for kits and assortment boxes

Assortment packs with a range of washer sizes in one box are great for DIYers who need a little of everything without predicting exact sizes.

Common mistakes and how to avoid them

Even seasoned DIYers slip up sometimes. Here’s what to watch out for so your fixings last.

Using too small a washer

A washer that’s too small concentrates load and can pull through. Always err on the side of a larger bearing surface when working with soft materials like thin sheet metal or timber.

Skipping corrosion protection

Outdoor screws and washers need to resist the elements. If it’s going outside, choose plated or stainless materials—think of it as weatherproofing your hardware.

Mixing incompatible materials

A brass washer on a steel bolt in a coastal environment can lead to galvanic corrosion. Match materials sensibly—stainless with stainless, plated steel with plated steel, and brass where conductivity matters.

Bulk buying and trade accounts

If you’re a tradesperson or run a small workshop, opening trade accounts with suppliers like Expert Electrical, RS Components, Screwfix, or Toolstation can unlock better pricing and bulk packaging. Buying in bulk not only reduces cost per washer but also keeps you stocked so jobs don't stall while you wait for parts.

Environmental and safety considerations

Choose materials that last to avoid premature replacements that add to landfill. Recycle metal washers where possible, and store packs in labelled, dry containers to prevent rust before use. When cutting or grinding washers, wear eye protection and dispose of metal filings safely.

Armed with these tips, you can confidently pick the right washer for any job—whether you grab a small pack at your local DIY store or order branded electrical hardware from a specialist supplier. The trick is matching size, material and finish to the task at hand and knowing where to look when you need a particular SKU or pack size.

Ready to sort your next project? Jot down the bolt diameter in inches, decide whether you need aesthetic or heavy-duty corrosion protection, and pick a trusted supplier. You’ll save time and avoid returns—plus your finished work will look and perform better.

Conclusion: Choosing the right washer is small detail that makes big differences. From Expert Electrical specialist packs to high-street options at Screwfix, Wickes or B&Q, the right washer in the right material and size will protect your work and keep assemblies secure for years.