If you’ve ever taken apart a bicycle brake caliper, fixed a loose cabinet handle, or even swapped out a light socket, chances are you’ve crossed paths with a star washer—though you might not have known it by name. As a supplier of precision washers, I get asked this question at least once a week by mechanics, hardware store buyers, and even weekend DIYers staring at a pile of small metal parts in a garage. Let’s break down what a star washer actually is, why it matters, and how it’s different from every other kind of washer you might have worked with. Washers
First, let’s start with the basics: what makes a star washer different from a flat washer, which is the most common type most people know. Flat washers are thin, circular discs with a hole in the middle, designed to spread the load of a bolt or nut across a surface to prevent scratching or damage. A star washer, by contrast, has sharp, pointed teeth (or “prongs”) cut into one or both sides of its flat base. Those teeth are the star’s defining feature—they’re what makes this small part so versatile for jobs where keeping a fastener from loosening is non-negotiable.
Wait, let’s get specific: there are two main types of star washers, right? Internal tooth and external tooth. I see people mix these up all the time. External tooth star washers have their teeth pointing outward around the outer edge of the washer. These work best when you’re attaching two metal parts together, because the outer teeth dig into both the bolt head/nut and the surface it’s clamping down on. Internal tooth star washers, on the other hand, have teeth pointing inward, around the inner edge of the hole. These are used when you want the teeth to grip the shaft of a bolt or screw, rather than the surrounding material. I remember a customer a few months back who came to us confused because his factory assembly line kept having bolts work loose from their conveyor belt rollers—turns out he’d been using external tooth washers when he needed internal tooth ones to grip the bolt shaft instead of the roller housing. That’s the kind of small detail that makes a big difference, and that’s what we focus on as a supplier.
Now, why are those teeth so important? The whole point of a star washer is to prevent what’s called “fastener relaxation”—that’s the annoying problem where a nut or bolt slowly spins loose over time, thanks to vibration, thermal expansion and contraction, or just regular wear and tear. Think about the wheels on a car: every time you drive over a pothole or a speed bump, the vibration tries to shake the lug nuts loose. A standard flat washer can’t stop that, because it’s just sitting there, spinning along with the nut. The sharp teeth of a star washer dig into both the clamped surface and the fastener itself, creating a tiny, almost unbreakable mechanical lock that stops that rotation. It’s not like a lock washer with those coiled springs, right? Those are another common alternative, but star washers are better for high-vibration applications where you need a compact, low-profile part—spring lock washers can take up more space and sometimes don’t provide as consistent grip over time, especially in high-temperature environments.
Let’s talk about materials, because that’s a huge part of what makes a star washer work for different jobs. As a supplier, we stock star washers in several common materials, each for a specific use case. Carbon steel is the most popular—it’s strong, affordable, and works great for general hardware, automotive, and construction applications. We also offer stainless steel star washers, which are essential for outdoor projects, marine equipment, or any job where corrosion is a risk. Stainless steel resists rust and saltwater damage, so that’s the go-to for boat trailers, dock hardware, or outdoor furniture. For specialty jobs, we even have phosphor bronze star washers, which are used in electrical applications because they’re non-magnetic and have good conductivity—great for wiring connections where you don’t want to risk interference or corroded parts messing up the electrical current.
I should also clear up a common myth: some people think star washers are only for heavy industrial jobs, but that’s not true. I’ve sold tiny, 1/8-inch internal tooth star washers to a customer who builds custom watches—those small gears need to stay locked in place, and a flat washer just wouldn’t cut it. On the other end, we supply 2-inch external tooth star washers for large construction cranes, where a single loose bolt could be a safety hazard. Size doesn’t matter as much as the application, and that’s why taking the time to match the right washer to the job is so important.
Let’s get into a real-world example, something most people can relate to. Last year, a local bicycle shop brought us a large order of 5mm external tooth star washers. The owner told me their repair techs were getting constant complaints from customers that their mountain bike handlebars would work loose after a few rides on rough trails. They’d been using flat washers before, and the vibration from bumpy terrain was enough to let the handlebar stem bolt spin. We suggested switching to external tooth star washers, and within a week, the shop said the number of loose handlebar complaints dropped to zero. That’s the kind of impact a small, simple part like a star washer can have—on safety, on customer satisfaction, on avoiding expensive repairs.
Now, let’s talk about when you shouldn’t use a star washer, because that’s just as important as when you should. A lot of DIYers grab a star washer from the hardware store because it looks like it will work, only to run into problems. You never want to use a star washer on soft materials like wood, plastic, or aluminum if you can help it—those sharp teeth will dig too deep, stripping the material or even cracking it. For soft surfaces, a flat washer paired with a different locking method, like a thread-locking adhesive or a nylon insert nut, is a better choice. Also, star washers aren’t designed to be reused. Once you remove a star washer, the teeth are flattened or deformed from digging into the surface, so they won’t provide the same lock if you put them back on. It’s always better to use a new star washer every time you disassemble and reassemble a fastener.
As a supplier, I’ve seen firsthand how often people overlook washers in general, treating them like an afterthought in a project or repair. But that’s a mistake. A star washer is a simple, low-cost part that solves a really frustrating, high-stakes problem: fasteners coming loose when you don’t want them to. Whether you’re building a custom engine for a race car, assembling medical equipment that needs to be reliable, or fixing a backyard gate that won’t stay closed, the right star washer can make the difference between a job that lasts a year and one that falls apart in a month.
If you’re working on a project and you’re not sure if a star washer is what you need, or if you’re looking for a consistent supplier that stocks the right sizes and materials for your application, don’t hesitate to reach out for a procurement conversation. We work with small DIY shops, large industrial manufacturers, and everyone in between, and we can help you pick the right part for your specific needs. No question is too small, no order is too large—we’re here to make sure you have the parts you need to get the job done right, safely, and on time.
Flat Washer References:
- Machine Design. "Selecting the Right Lock Washer for Vibration and High-Temperature Applications." Society of Manufacturing Engineers, 2022.
- ASME B18.21.1. "Standard for Lock Washers." American Society of Mechanical Engineers, 2019.
- Marine Hardware Association. "Corrosion-Resistant Fasteners and Washers for Marine Environments." MHA Technical Bulletin, 2021.
- ISO 7089. "Plain Washers—Series Normal, For Use with Screws and Bolts." International Organization for Standardization, 2020.
Jiaxing Jinling Hardware Technolgy Joint Stock Co., Ltd.
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