M4 304 Stainless Steel Penny/Flat Washers (50 pcs) for Bolts & Screws

The essentials

If you’re putting together a fix that needs to stay put—especially outside—small metal washers can make a surprising difference. These M4 washers are made from 304 stainless steel and come as a set of 50 penny/flat-style washers. They’re designed to spread the load under an M4 bolt or screw and help reduce loosening over time.

On paper, the appeal is pretty straightforward: stainless steel for corrosion resistance, plus a larger contact surface that can ease pressure on the parts you’re clamping together. They’re not a miracle cure for every mechanical problem, but they’re a sensible “belt and braces” add-on for many common DIY and light industrial jobs.

What they’re for (and why a washer matters)

A flat washer basically sits between the fastener head and the material. That extra layer increases the contact area, so the tightening force is distributed more evenly. In real-world terms, that can mean less risk of damaging softer surfaces and fewer instances of the fastener gradually working loose.

These M4 stainless washers are also positioned as friction-reducing and leak-preventing in certain set-ups. Whether you’ll actually notice that depends on what you’re fastening (and what you’re fastening to), but the concept is the same: smoother clamping and better long-term holding power.

Key points on the build

Made from 304 stainless steel, these washers are described as stable, corrosion- and rust-resistant, and resistant to breaking or deformation. That matters if your project sees damp conditions, weather exposure, or general outdoor use.

The design is also described as high precision, with sizing referenced as M4251.5. While you shouldn’t treat that as a substitute for measuring your specific bolt/screw and the mating hardware you have, it does suggest the washers are intended to fit neatly into common M4 applications rather than being a random “close enough” spacer.

Where they shine in everyday use

These washers are presented as multi-scenario parts, covering things like electrical connections, household mechanical equipment, mechanical parts, home maintenance, and even automobile and ship applications. That broad list is basically a hint at the target category: general-purpose stainless washers for people who want a reliable standard part they can use again and again.

A practical example: if you’re reassembling an outdoor electrical enclosure or a small bracket that’s exposed to rain, using stainless washers under M4 fasteners can help the connection hold its clamp load better and resist corrosion compared with plain mild-steel washers.

What you should double-check before buying

A limitation to keep in mind: this is for M4 fasteners, not a universal size. If your bolts or screws are a different thread size, these won’t be the right fit.

Also, the description talks about preventing loosening and reducing friction, but the exact performance will depend heavily on the rest of your joint—material type, how you tighten, vibration levels, and whether there’s an additional locking method in play (for example, the rest of the hardware package you’re using).

Who it suits (and who should skip it)

It’s a good fit if you want 304 stainless steel washers for M4 screws/bolts and you’re working on outdoor or corrosion-prone projects where basic clamping and load distribution matter. It also makes sense if you simply want a small, repeatable part for maintenance jobs—because having spare washers on hand is one of those unglamorous habits that saves time.

It may not suit you if you need a different bolt size, or if your application specifically requires a more specialised washer/locking solution (in cases where loosening risk is extreme, you may need more than a standard flat washer). And if you’re working purely indoors on very stable joints, the stainless upgrade may be more than you actually need.

Is it worth it?

Buy these M4 304 stainless steel penny/flat washers if you’re building or repairing a threaded connection and want a corrosion-resistant washer that helps spread load and support a more secure clamp over time. They’re particularly reasonable for outdoor use and routine maintenance where having the right standard part to hand pays off.

Avoid them if your project doesn’t use M4 fasteners, or if you’re expecting the washer alone to solve every loosening problem under heavy vibration. In those scenarios, it’s worth looking at the overall fastening strategy rather than relying on one component.

Mini FAQ

Will these fit M4 screws and bolts?

They’re described as M4 washers for screws/bolts, so they’re intended for M4 fasteners. If you’re unsure, check the thread size and the washer dimensions before fitting.

Are they suitable for outdoor projects?

Yes, the description specifically calls out long-term outdoor work and stainless corrosion resistance.

What do penny/flat washers do in a joint?

They sit under the fastener head to spread the load over a wider area, which can help reduce loosening and protect the parts being clamped.

How many washers do I get?

You get 50 pieces in the pack, per the product listing title.