Hey there! If you’ve ever stared at a parts sheet for your next project, squinted at the line that says “press-in fastener,” and wondered, “Wait—exactly how many sizes do I even have to choose from?” then this post is for you. As a press-in fastener supplier, I get it. Most folks don’t think twice about these tiny workhorses until they’re mid-assembly and realize the one they grabbed is way too small or too big, and now they’ve got a line of half-built products and a headache. Today, we’re breaking down every size you can actually get, no jargon, no fluff—just real talk about what’s available, who needs it, and why picking the right one isn’t just overcomplicating things. Press-in Fasteners
First off, let’s get one thing straight: press-in fasteners aren’t a one-size-fits-all thing. If you only need to fasten a flimsy plastic housing for a smart watch, you don’t need the same size as a bracket holding a car door to its frame. The sizes follow standard specs, but there’s also a ton of custom stuff for weird, specific projects, so don’t ever think “I can’t get this exact size.” Let’s start with the most common category everyone deals with—standard metric and inch sizes, because that’s where 90% of the work happens.
Metric sizes are the bread and butter for most manufacturing these days, and the ones you’ll see day-to-day range from M1.6 all the way up to M8. Wait, that’s a range, but let’s get specific. The smallest ones, M1.6, are basically for tiny electronics—think wearables, camera internals, small PCB fasteners. These are like, what, 1.6mm in diameter? Super tiny. You’ve got to handle them with tweezers, basically, because if you drop one, it’s gone forever. We make these for clients that build wireless earbuds, fitness trackers, even small medical devices like glucose monitor cases. They press into thin plastic or thin aluminum (like 0.5mm to 1.5mm thick) and hold enough force for those light, low-vibration applications.
Next up, M2 to M5. These are the workhorses. If you’re building laptops, smartphones, home appliances, or small automotive parts, this is your sweet spot. M2 is for things like laptop keyboard shields or small circuit board mounts. M3 is probably the most used size out there—we sell more M3 press-in fasteners than any other. Clients use M3 for everything from mounting fans in desktop computers to attaching interior trim in cars, and even building small robots. The thickness of the material here is usually between 1mm and 4mm. M4 and M5 are for a little heft—bigger plastic enclosures, power tool housings, motor mounts, stuff that needs a little more holding power without being too bulky.
Then we’ve got the larger metric sizes, M6 to M8. These are for heavy-duty stuff. If you’re making industrial equipment, agricultural machinery, truck parts, or even large furniture that’s built like a tank, this is where you look. M6 is common for mounting larger panels, tool bases, or HVAC components—material thickness here is usually 3mm to 8mm. M8 is the heavy hitter. We supply M8 fasteners for things like trailer frames, construction equipment brackets, and even some aerospace secondary structures. These can handle way more torque and vibration, so they need to be pressed into thicker materials—like 5mm up to 12mm of aluminum, steel, or thick molded plastic.
Now, let’s talk inch sizes, because a lot of older equipment, automotive parts built in the US, and custom projects still use imperial measurements. These range from #2-56 up to ½ inch. The tiny inch sizes, #2-56 and #4-40, are basically the imperial version of M1.6 and M2. They’re used for old electronics, classic car restorations, and small prototype parts. #6-32 is similar to M3, the go-to for a lot of general assembly. #8-32, #10-24, and #¼-20 are the mid-range, used for everything from small engine parts to furniture hardware to enclosure mounts. Then the big ones: ⅜-16 and ½-13. These are for heavy-duty imperial applications, like large machinery, truck chassis, and structural parts that still use inches.
But wait—those are just the standard, off-the-shelf sizes. What if your project is weird? Like, you need a fastener that’s not a standard diameter, or a length that’s not in the catalog? I get that. We get calls all the time from startups building something totally new—maybe a foldable drone that needs a custom fastener to fit in a narrow hinge, or a medical device that has a weirdly thick plastic housing. Custom sizes are totally doable. We can make press-in fasteners with diameters anywhere from 1mm up to 15mm, and lengths from 2mm up to 25mm. No, that’s not a random number—we’ve tested that range, so we know it works. The key here is that custom sizes aren’t just for big clients; startups, small machine shops, even hobbyist projects? We’ll work with you. I’ve had a customer come to us with a one-off prototype for a custom bike frame that needed a press-in fastener no one made, and we knocked it out in a week for them. No hoops, no extra fees that make you want to pull your hair out.
Now, here’s something a lot of people miss when they’re checking sizes: it’s not just the external diameter and the length. You also have to pay attention to the “body diameter” and the flange, if it has one. Wait, let’s keep this simple. The external diameter is the size you’d measure with a caliper from the outside of the fastener, that’s the one we’ve been talking about. The body diameter is the part that actually presses into the hole in your material. And the flange—if there’s a flat ring around the head—sits on the surface of your part, keeps the fastener from sliding all the way in, and distributes the pressure so your plastic or thin metal doesn’t crack. That’s super important for materials that are brittle, like thermoplastics or thin aluminum. If you get a fastener with the wrong flange size, it’ll either pull through your material or sit funny and not align with whatever you’re fastening to.
Another thing that affects size compatibility is the material you’re pressing into. Let’s say you’re working with thin, flexible plastic—you don’t want a super large diameter fastener, because it’ll stretch the plastic too much and loosen over time. But if you’re working with thick, rigid steel, you can go bigger, because the material can handle the pressure. We always ask customers to tell us what their base material is, how thick it is, and how much vibration or torque the assembly will see, because that tells us exactly what size will work, not just what’s in the catalog. I’ve had a client come in insisting they need an M5 fastener for a 1mm thick plastic part, and we told them they’d be better off with an M3 with a wide flange—same holding power, no cracking. That’s the kind of thing suppliers don’t always tell you, right? We’re not here to just sell you the biggest size; we’re here to sell you the right size for your project.
Wait, let’s talk about thread size too, because that’s part of the whole “size” thing people overlook. A press-in fastener’s thread has to match the screw you’re using. So if you’re using an M3 screw, you need an M3 press-in fastener. Easy enough, but sometimes people mix up pitch. For example, M3 has a standard pitch of 0.5mm, but there’s also a fine pitch M3 with 0.35mm. If you mix those, the screw won’t thread right. Same with inch sizes: #8-32 is 32 threads per inch, #10-24 is 24. That’s a common mistake, especially for people switching between metric and imperial. We always flag that when customers order, but it’s good to know going in, because ordering the wrong thread pitch is a way bigger headache than ordering the wrong external diameter.
Now, what about for specialty applications? Like, if you’re working with extreme temperatures, or corrosive environments, or food-grade materials, does that change the available sizes? Short answer: no, the sizes are still the same, but the material of the fastener might change, but that’s a separate call. Wait, no—the size range doesn’t shift. We still make M1.6 to M8 metric and #2-56 to ½-inch inch sizes, even for stainless steel press-in fasteners for food processing equipment, or titanium ones for aerospace where weight is a factor. The only time sizes are adjusted is for things like micro-press fasteners for tiny sensors, which go down to 0.8mm, but that’s a super niche product. We don’t advertise those a lot because most customers don’t need them, but if you’re building a tiny sensor for a drone, we’ve got you.
Let me give you a quick example of how size choice goes wrong. A few months back, a guy from a small appliance company called me panicking. They’d been buying M4 press-in fasteners for their blender housings, and after testing, half of them were pulling out during testing—blend testing, I guess, with all that vibration. Turns out, they were using M4 fasteners in 1.5mm thick polypropylene, which is pretty flexible. We suggested bumping up the flange size on an M3 fastener, so the body was still M3, but the flange was wider, distributing the pressure more evenly across the thin plastic. It worked like a charm. They stopped having pull-outs, and didn’t have to retool their whole assembly line to use a different diameter. That’s why size isn’t just a number—it’s matching the fastener to your specific part, not just the spec sheet.
Now, if you’re still here, and you’re thinking, “Okay, so what size do I actually need for my project?” here’s the quick cheat sheet:
- Tiny electronics (wearables, PCB mounts): M1.6, M2, or #2-56, #4-40. Material thickness <2mm.
- General assembly (laptops, small appliances, robot parts): M3 or #6-32. Material thickness 1-4mm.
- Heavy general (power tools, automotive interior, furniture): M4, M5 or #8-32, #10-24. Material thickness 2-6mm.
- Industrial/heavy duty (trucks, equipment, large panels): M6, M8 or ⅜-16, ½-13. Material thickness 3-12mm.
But again, this is just a cheat sheet. The only way to be 100% sure is to talk to someone who knows press-in fasteners. That’s where we come in. We don’t just send you a catalog and say “pick one.” We ask questions: what’s your part made of? How thick is it? How much vibration or weight will it handle? Do you have space constraints? And then we tell you exactly what size works, and even suggest tweaks (like a wider flange, or a specific material) that make the fastener work better for your project, no extra cost.
Wait, one last thing: lead times. A lot of people think if they need a custom size, they’re looking at 4-6 weeks. But we keep a lot of common custom sizes in stock, and if we don’t, we can turn around a custom run in 7-10 business days. For startups with tight prototype timelines, that’s a game-changer. I’ve had a customer need 50 custom press-in fasteners for a prototype that had to be at a trade show, and we had them ready in 5 days. No overcharging, no excuses.
At the end of the day, press-in fasteners are small, but they make or break an assembly. Picking the right size isn’t just checking a box on a parts list—it’s saving you from rework, broken parts, and wasted time and money. If you’re working on a project and you’re not sure what size you need, or you can’t find the exact size you’re looking for, hit us up. We’re here to help, no strings attached, no confusing sales pitches, just real advice for real projects.
Screws REFERENCES
- Industrial Fasteners Institute. (2022). Press-In Fastener Design and Application Guidelines.
- Society of Automotive Engineers. (2021). Standard for Threaded Fasteners for Lightweight Assembly.
- International Organization for Standardization. (2020). ISO 10664: Fasteners for Threaded Insertion in Plastics.
- Aerospace Industries Association. (2023). Guidelines for Fastener Size Selection for Secondary Aircraft Structures.
Changzhou Unilee Fastening Technology Co., Ltd.
With abundant experience, we are one of the most professional press-in fasteners manufacturers and suppliers in China. Please feel free to buy premium press-in fasteners made in China here and get pricelist from our factory. All customized products are with high quality and competitive price.
Address: Building 32, No.158, Jinchuang Road, Economic Development Zone, Changzhou City, Jiangsu Province
E-mail: vitatree.cn@gmail.com
WebSite: https://www.unileefastener.com/
