Screws meant for plastic. - Page 1
Forum section: electronics / general

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: December 22, 2024, 09:43:36 pm
content: I'd like to buy an assortment of small-ish Plastite-style thread forming or thread rolling (I don't know what the difference is but I want specifically screws for plastic)I've attached a picture of a screw used to hold a PCB to the front panel of a Commodore 1571 drive. It seems to be a 5/16" 2-28 Trilobular.https://www.amazon.ca/gp/product/B00GDXU4WM/ref=ox_sc_act_image_1?smid=A3DWYIK6Y9EEQB&psc=1but I don't want a 100 of one type, I'd be happy with 10 or 20 and with many other sizes.I'm a bit surprised that I can find screws for pretty much everything else, but not for screwing into plastic. You'd think with all the 3D printing *someone* would need plastite screws at some point...

author: TimFox
author_rank: Super Contributor
timestamp: December 22, 2024, 09:53:08 pm
content: Here's McMaster Carr's collection of screws for plastic:https://www.mcmaster.com/products/screws/tapping-screws~/Go to almost the bottom of the page for the plastic-use screws.

author: jfiresto
author_rank: Frequent Contributor
timestamp: December 22, 2024, 09:55:14 pm
content: Here is perhaps a little, usefulreading material.

author: edpalmer42
author_rank: Super Contributor
timestamp: December 22, 2024, 11:06:00 pm
content: Quote from: TimFox on December 22, 2024, 09:53:08 pmKeep in mind that if you're outside the U.S., McMaster Carr doesn't sell to hobbyists or individuals, only to businesses."In addition, if you are located outside the United States, you represent and warrant to us that the Products are being purchased only for professional or commercial use, and not for personal or household use."They also say that Australia & New Zealand customers must state that they have a National Business Number and GST Registration.I can't find it now, but at one time they stated that they wouldn't ship to Canadian residential addresses. Period.Ed

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: December 23, 2024, 03:23:13 am
content: I think anybody's money is good at Misumi. You might find what you want under their micro-screw category, though it won't say made for plastic. If you look at them, they're about what you need. I think some are tri-lobe, which is common for plastics. The site is huge so I may have missed something. The only problem is you'll end up buying more than you probably want, but they tend to be inexpensive. You probably won't find anybody willing to get up in the morning to sell 20 screws.https://us.misumi-ec.com/

author: Whales
author_rank: Super Contributor
timestamp: December 23, 2024, 04:03:29 am
content: Why do do you want the triangular/plastite shape? I mostly see plastic goods & appliances using standard (round) screws for untapped plastic holes.I personally use No.6 screws (OD vaguelly ~3mm, ID~2.5mm) in my 3d printed parts and they go in well and hold really well. For bigger parts I use No. 8 (OD~4.2mm).

author: jfiresto
author_rank: Frequent Contributor
timestamp: December 23, 2024, 08:38:09 am
content: Quote from: Whales on December 23, 2024, 04:03:29 amThere are two types of screws for plastic (see my above link), akin to cutting taps and form/roll taps for hard and soft materials. Are the screws you are seeing for hard plastics?

author: Shay
author_rank: Regular Contributor
timestamp: December 23, 2024, 06:23:15 pm
content: Quote from: Alex Eisenhut on December 22, 2024, 09:43:36 pmIt's called self tapping screws. A quick search on AliExpress reveals about million options.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: December 24, 2024, 03:36:07 am
content: Self tapping screws almost invariably refer to screws meant for metal. For plastic it's another story.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: December 24, 2024, 06:31:14 am
content: I have been able to purchase 20 screw quantities of screws for plastic from SCREWERK.COM. Don't know how happy they are about it, but didn't get any complaints. I did order five different sizes since I couldn't figure out exactly which one was correct.

author: Shay
author_rank: Regular Contributor
timestamp: December 24, 2024, 09:02:03 am
content: Quote from: Alex Eisenhut on December 24, 2024, 03:36:07 amSelf tapping screws for metal? Never heard of those, maybe you mean self- drilling screws.From Wikipedia:"A self-tapping screw is a screw that can tap its own hole as it is driven into the material. More narrowly, self-tapping is used only to describe a specific type of thread-cutting screw intended to produce a thread in relatively soft material or sheet materials, excluding wood screws"Anyhow, when searching on AliExpress almost all results for "self tapping screws" are screws intended for plastic.https://a.aliexpress.com/_oEPXXEP

author: tooki
author_rank: Super Contributor
timestamp: December 24, 2024, 09:19:41 am
content: Quote from: Shay on December 24, 2024, 09:02:03 amNo, Alex is 100% correct.“Soft material” includes things like aluminum and zinc, and “sheet materials” includes sheet metal, most commonly steel. But that isn’t the whole definition given on the page, either.Trust me, to us native English speakers (or at absolute minimum, in North America), when we hear “self-tapping screw”, the first thing we think of is sheet metal screws and screws for solid, soft metal (like aluminum), because metals are materials where machine screws can also be used, so the distinction between machine screw and self-tapping screw is fundamental. Because plastics comparatively rarely use machine screws, when we hear “screws for plastic”, we assume self-tapping screws.In English (and for that matter, in German, the other language I speak at a native level), we never use “self-tapping” to describe screws for materials where screws arealwaysself-tapping, because it’s redundant. So wood screws, plywood screws, drywall screws, etc. are called just by those names, without needing to specify self-tapping. As I said above, screws for plastics almost fall into this category, since machine screws are seldom used in plastics without metal threaded inserts. So in practice, we really use “self-tapping” as a descriptor for the material where both machine screws and self-tappers are common, and that is metal.A self-drilling screw is a special subset of self-tapping screws that don’t require a pilot hole.Quote from: Shay on December 24, 2024, 09:02:03 amI can’t believe this needs to be restated so often, butAliExpress is not in any way indicative of standard English terminology for things.Those are often machine translations, and even when they’re not, they often use terminology that is wildly divergent from the terminology used by native speakers. Additionally, sellers employ tons of “keyword stuffing” to make their listings show up in as many searches as possible, so the keywords used are often not only incorrect, but irrelevant to the product being sold.And to boot, your claim that “almost all results” for them on AliExpress are screws intended for plastic isn’t even true! Many are wood screws (which, as I explain above, are never called “self-tapping” in English), many are sheet metal, and many do not specify at all — and among those unspecified ones, some look like they’re for plastic, some look like sheet metal screws, and many look like wood screws.

author: SteveThackery
author_rank: Super Contributor
timestamp: December 24, 2024, 09:31:24 am
content: Quote from: Shay on December 24, 2024, 09:02:03 amEdit: Oops - simul-post with @tooki.No, he means self tapping. They are incredibly common and yes, they were originally intended for metal. To be specific, for sheet metal and sometimes solid aluminium (they won't self-tap into a solid block of steel). I've taken loads of consumer electronic products to bits, and the outer case is quite commonly attached using lots of self tappers going through a pre-drilled hole in the outer case and into a pre-drilled, but slightly smaller, hole in the chassis. The screw makes it's own thread in the chassis hole the first time it is screwed in. The thickness and type of chassis material is important: sheet aluminium can be thicker than sheet steel.You can also get self-tapping screws for plastic, and actually they are much more common now that plastic enclosures are used for almost everything. I'm no expert, but I imagine the thread form of the self-tapping screw will be different from one intended for metal, what with plastic being (generally) much softer.Having said all that, in reality plastic does seem incredibly tolerant, and I suspect you can get a perfectly adequate fix using almost any old screw with a coarse thread on it - even a wood screw. One danger is that some plastics under too much stress will gradually develop cracks, so the 1/2 inch #6 wood screw that seemed to work OK to start with might not in the long run.

author: tooki
author_rank: Super Contributor
timestamp: December 24, 2024, 09:54:08 am
content: Quote from: SteveThackery on December 24, 2024, 09:31:24 amI then edited my post to add a lot more info, FYI.Quote from: SteveThackery on December 24, 2024, 09:31:24 amTake a look at the link jfiresto posted earlier, it goes into the design of plastics screws:Quote from: jfiresto on December 22, 2024, 09:55:14 pmBut in a nutshell, for a given screw size (outer diameter of the threads, the major diameter), the minor diameter (diameter of the “core” or “root”) of screws for plastic is significantly smaller than for wood screws and self-tappers for metal, allowing much deeper thread engagement. The shape of the threads is also different.Quote from: SteveThackery on December 24, 2024, 09:31:24 amUsing other screws, especially wood screws, in plastic risks splitting open the screw boss (if using screws with the same outer diameter) because the inner core of the screw is much larger. And if you use a screw with the same root diameter, the non-plastics screw threads won’t engage very securely.

author: Shay
author_rank: Regular Contributor
timestamp: December 24, 2024, 10:41:08 am
content: Quote from: tooki on December 24, 2024, 09:19:41 amThanks for your enlightenment. I’m used to think that self tapping screws and for both plastic and wood but not for metal or aluminium. Now I know it is more like a family.It seems it is easy to know on AliExpress which screw is for plastic by looking at the thread angle and pitch and that there is no tip like screw used for wood. Maybe it is good enough for op application if it is not critical nor for production.

author: tooki
author_rank: Super Contributor
timestamp: December 24, 2024, 10:49:55 am
content: Quote from: Shay on December 24, 2024, 10:41:08 amWas that not obvious from reading the Wikipedia article about them?! Or did you quote the article without even skimming it first? On second thought, it’s obvious you didn’t read the article at all.And to reiterate: while wood screws (and others I listed above) do technically tap their own threads, we don’tcallthem self-tapping because there is no need to. So we really only say “self-tapping” for the situations wherebothself-tapping and machine screws exist, and 99% of the time that means metal.Quote from: Shay on December 24, 2024, 10:41:08 amPlease read the page jfiresto linked above. It goes over the types and differences.It’s not just thread angle and pitch, it’s also the minor diameter and the threadshape. Screws for plastic exist both with pointy tips and with blunted tips. A quick glance is oftennotenough to determine what type of screw it is, and the AliExpress listings frequently don’t actually include enough speculations to make that determination.

author: T_guttata
author_rank: Regular Contributor
timestamp: December 24, 2024, 10:52:07 am
content: You can buy screws specifically for plastics from Bambulab:https://eu.store.bambulab.com/en-ch/collections/screws?page=2&srsltid=AfmBOoqLRPkW_e9v4lnm3wgKgp8yo24CU5kq1Uxu7a0htvpn761wkvd6As with all parts from Bambu, quality is very good and price is fine.

author: Shay
author_rank: Regular Contributor
timestamp: December 24, 2024, 11:20:57 am
content: Quote from: tooki on December 24, 2024, 10:49:55 amThank you for your detailed explanation. I admit I didn’t initially grasp the nuances of how self-tapping screws are categorized and how the terminology is used in different contexts, especially for metals. The distinction you’ve pointed out makes a lot more sense now, particularly why “self-tapping” is emphasized for screws intended for metal applications where machine screws are also an option.As for identifying screws for plastic, you’re absolutely right—relying solely on visual cues like thread pitch or the presence of a point can lead to mistakes, especially with incomplete specifications on marketplaces like AliExpress. I’ll take your advice and read through the linked page to better understand the differences in thread shapes and minor diameters.

author: WattsThat
author_rank: Frequent Contributor
timestamp: December 24, 2024, 03:26:55 pm
content: Another US source for similar hardware ishttps://www.microfasteners.com/

author: CatalinaWOW
author_rank: Super Contributor
timestamp: December 24, 2024, 04:47:50 pm
content: Just to compound your difficulties, the selection of plastic screws by material type assumes insertion in new, molded material. Properties of many plastics change with aging, and of course 3D printed objects are also different.In many cases the pull out strength required is small. If you are working on older equipment it is wise to start with a smaller size screw, displacing the minimum material. If it doesn't hold adequately you can always move up. But if the plastic breaks when trying a screw that is too large for the current material properties the repair difficulty jumps a lot. In cases where more than the typical ten insertions have occurred and the hole is stripped the classic woodworking techniques of filling or shimming can work if done cautiously. The ten insertion limit can also be extended if you carefully align the screw with the existing displaced "threads".

author: jfiresto
author_rank: Frequent Contributor
timestamp: December 24, 2024, 05:11:18 pm
content: Quote from: CatalinaWOW on December 24, 2024, 04:47:50 pmLubricating the screw with some beeswax probably would not hurt.

author: mikerj
author_rank: Super Contributor
timestamp: December 24, 2024, 09:50:10 pm
content: I went through the same search for plastic screws recently, they are quite difficult to find but using the search terms "thread forming" and "thread rolling" got me results in the UK. I see some suppliers in the US, and Grainger in Canada but there are surely others:https://www.valuefastener.com/screws/thread-rollinghttps://apexfasteners.com/fasteners/thread-forming-screws/thread-forming-screws-for-plastichttps://www.grainger.ca/en/category/thread-cutting-thread-forming-screws/drilling-tapping-screws/c/11771

author: Infraviolet
author_rank: Super Contributor
timestamp: January 03, 2025, 08:20:51 pm
content: It's a bit late to add this to the thread but:I'd usually tend to say that screws forming threads in to plastic is better avoided. Usually it is a wiser move to create a space in the plastic part in to which a nut can be placed, or otherwise to have a place where heat-staked threaded inserts can be placed. Threads formed directly in to plastic can be pretty weak, and very much prone to wearing down after more than one or two insertion and removal cycles. Both hex shaped volumes to but actual nuts in to, and cyclindrical volumes to melt threaded inserts in to, give you metal-on-metal threading and distribute the stresses than enter the plastic over a much wider area.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: January 04, 2025, 12:21:01 am
content: Quote from: Infraviolet on January 03, 2025, 08:20:51 pmAll of that is true, but ignores the fact that many applications don't require much strength, aren't expected to be removed even once, let alone often and benefit from the lower cost involved with a thread forming screw. And this isn't just for cheap throw away consumer goods. Think of single use medical goods, or radiosondes or many other things.I am currently tuning up an at least 20 year old large format printer. Most of the covers are attached with thread forming screws. And that aspect of the printer is still working fine, through multiple repair cycles. I am glad that the manufacturer put the money into accuracy in the print engine, not into overdesigned cover attachments.The best design choice is a compromise between all of the requirements.

author: tooki
author_rank: Super Contributor
timestamp: January 04, 2025, 12:18:39 pm
content: Quote from: Infraviolet on January 03, 2025, 08:20:51 pmI mean… metal threaded inserts and nuts are nice, but let’s be realistic, screws directly into plastic are used in probably 99% of applications because for most things they’re good enough.If it’s high quality plastic and one treats the threads with care, you can certainly get way more than one or two cycles out of it.

author: Kean
author_rank: Unknown
timestamp: January 06, 2025, 03:23:33 pm
content: And the metal threaded inserts don't always give a better result - like on my 3D printer lid where the inserts have come loose in the bosses.Two out of four of the bosses have cracked, and all four inserts fell out.Yes, that is mostly a design issue, but PT screws likely would have been fine under the stress of opening and closing the lid (unlikely to get unscrewed often, it at all) and would not have required such a large hole in the plastic boss thus making them so weak.