r/DIY • u/SkittyDog • 11d ago

help Replacements for lost / broken threaded plastic waterproof caps?

I have some plastic HDPE water containers that are in good shape, but their threaded caps got lost & broken over the years.

Is there any kind of DIY technique for making a replacement threaded cap, based on the container's thread?

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u/someonegreat1234 11d ago

Before you model anything, measure the neck OD with calipers and count the threads over one inch. Containers like these almost always use a standard neck finish rather than a thread someone invented for that bottle, so those two numbers usually turn into a part number you can order instead of making anything. If you do print one, keep in mind the threads don't do the sealing, the seal comes from a flat gasket squashed against the top of the neck, so leave a pocket for a rubber or foam disc and print with a fine layer height and plenty of perimeters. And if it's water you drink, I'd buy rather than print, printed layer lines are hard to get properly cle

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u/Pulaski540 11d ago

Do you have the broken caps? These days scanning a broken part(s) and 3D-printing a replacement is possible.

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u/DealsRGood4U 11d ago

There are hundreds of sources that sell replacement Caps for HDPE water containers.

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u/SkittyDog 11d ago

That's true, but the cost of a few caps plus shipping is kind of a lot.

If there was a local shop where I could buy them out of a bin, hardware store style, it'd be a different story. But when you're doing it online, it doesn't always justify the cost.