Learn The Secrets Of Matching Bottle Cap Threads To One Another

Do you want to design something to match existing threads on a bottle, or a cap? It turns out there’s an easier way than reaching tiredly for the calipers and channeling one’s inner reverse-engineer. Bottle cap threads — whose industry term is the neck finish — aren’t arbitrary things; they are highly standardized, and [Noupoi] researched it all so that you don’t have to! The Bottle Cap Thread Calculator takes a few key measurements and spits out everything needed to model exact matches. Need some guidance on how exactly to use the information the calculator spits out? There is a handy link to a Fusion360 tutorial on creating bottle threads (YouTube video) to demonstrate.

This all came from [Noupoi] wanting to model an adapter to transfer the contents of one bottle to another, smaller bottle. By identifying which thread was used on each bottle, the job of modeling a matching adapter was much easier. It turns out that the bottle necks were an SP 28-415 (larger) and a 24-415 (smaller), and with that information the adapter was far simpler to design. If you want to check the adapter out, it’s available on Thingiverse.

If truly reverse-engineering bottle threads is needed, here’s a method we covered that involves making a simple cast and working from that.

[via Reddit]

24 thoughts on “Learn The Secrets Of Matching Bottle Cap Threads To One Another

  1. Nice, but still involves a lot of manual fiddling to get the end result in fusion360.

    I hope this evolves into a plugin with a stupid simple guide on identifying the thread in a few steps (“measure this, then this, … done”) and it spits out a neck/cap thread directly inside fusion360, similar to how we can already create M-threads or any of the threads available in the McMaster-Carr component library by picking from a list.

    For OpenSCAD there is threadlib with which it is super easy to make PCO-1881 (PET plastic soda bottle threads).

  2. I use OpenSCAD for modelling since i have a “programming mind” and it’s so easy to modify the design by changing parameters. In OpenSCAD there is a perfect library for threads: https://github.com/adrianschlatter/threadlib
    it supports:
    * Metric threads (coarse, fine, and super-fine pitches) M0.25 to M600
    * Unified Inch Screw Threads (UNC, UNF, UNEF, 4-UN, 6-UN, 8-UN, 12-UN, 16-UN, 20-UN, 28-UN, and 32-UN). All threads are class 2 threads.
    * BSP parallel thread G1/16 to G6
    * PCO-1881 (PET-bottle thread)

    So recently i wanted to use a wine bottle as water reservoir for a bird drinker, designed a small adapter to have it stand upside down in a water bowl, this is all that takes:

    nut(“M30x2.5”, turns=4, Douter=36);
    specs = thread_specs(“M30x2.5”);

    difference() {


    1. Yah, I don’t really get why people would want to use anything else for designing parts. We can write one parametric file and then get a lifetimes worth of any variation we ever need on that part just by changing a few variables. Why would anyone ever want to use a manual CAD program?

      But then I’m a programmer by day so it’s already familiar to me.

      Don’t try to tell me though that for someone just starting out with experience in neither programming nor traditional CAD those other tools are easier to learn though. I’ve tried to figure out how to make small changes to things I found online both in Fusion 360 and FreeCAD. Both felt a little like sitting down in front of the console of the space shuttle and being told to land or die with no training.

      1. I know why you’d want to use something else, and I use OpenSCAD pretty much exclusively. Extrusions are awkward, doing constraints (this face touches that face) require a library and some practice…

        But things like gears, screws, and massaging tolerances to get things “just right” are awesome. And that’s what I do more of than anything else. So I suck it up and do some trigonometry on paper sometimes where it would be a matter of mouse-wiggling in another package. But that’s the cost of effortless screws and monstrously simple part reuse.

        I should really look into FreeCAD, which seems to blend the best of OpenSCAD with the other modalities, but I’ve never taken the time to dig in… So I guess OpenSCAD isn’t that limiting after all. :)

  3. Material matters – finish threads for plastic containers and glass may have different cross section profiles – search “”GPI” or “SPI” finish” for more details. When you get into lug closures or roll-on finishes, they may also be different. If you try to mate a plastic-threaded container with a glass-threaded fitting or vice versa without accounting for this, you may have a bad time.

  4. The calculator is good access to the bottle thread standards. In FreeCAD (0.19, didn’t try in older revisions…), I just open the ThreadProfile workbench, enter the numbers from the calculator presets and bang, threads. Sweet. :)

  5. Fusion is good at alot of things but sadly as far as threads go it kinda sucks as it can only handle single flute threads. (Sure you can model a custom yourself but kinda defeats the point of easy and using the thread tool.) As an example one common thread most people come in contact with that fusion cant do using its generator is the threads on mason jars.(this is actually multiple standards depending on what part of the world you are in)

  6. A low tech way is to wrap some PTFE tape (normally used for pipe threads) over the threads and put epoxy putty on it. It will mold pretty nicely to the threads, and the PTFE makes sure you can still get it off after the epoxy has hardened.

    1. You can make a kind of putty with ground ABS and MEK, though it’s better to build a few thin layers first. Then it dries out and leaves just the ABS. So that could work with the thread tape.

      As could that technique of using blow moulded bottles as heat shrink, just use a slightly oversize, or close fit on the biggest, pill bottle and heatshrink it on.

      Another option would be those self welding repair tapes.

  7. If you’re pouring stuff from one bottle to another using a fixed adapter between, how do you take the adapter off? Since it’s a straight piece, you’ll always have one bottle upside down, or both bottles sideways, and both cases cause you to spill liquids as you unscrew the adapter.

    It seems entirely pointless, unless you’re trying to catch the last drops from a soap bottle (protip: add a slosh of water and shake).

    1. yeah, if you cut a bottle it becomes a funnel. and then that funnel can be secured to another bottle using an adapter designed with help from these assistant calculation utilities.

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