38mm 3-Start Bottle Neck Cap Adapter for PET Bottles

Design preview. Rendered from the file, not a photo.

The maker says it fits: PET bottles. See the proof

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What it does

Shaped to fit the 38mm 3-start neck standard so it pairs with regular HDPE caps
Made for DIY bottle projects so you can build your own water dispenser
Works as a bottle connector shape so you can link containers for plant watering
Sized to the 38mm 3-start closure used on fruit juice and flat beverage bottles

How do you turn a plain container into a working bottle for your own DIY project? This neck adapter gives you a 38mm 3-start opening, shaped to match the same closure used on many fruit juice and flat beverage bottles. That means you can pair it with a regular HDPE cap you already have on hand.

This piece is built around the 38mm 3-start standard, one shape from a bigger family of neck and cap designs. It is made for people who like to build their own containers for water dispensers, plant watering setups, or other bottle-based projects. The threads follow the 3-start pattern so a standard cap can turn onto it.

Use it on your own container build and screw on a cap you already own. It is a simple physical piece meant to bring PET bottle style closures to projects where they are not normally found.

7.9k downloads in the maker community. That is interest in the design on the site it came from, not our sales.

What it fits

The maker says it fits: PET bottles

That is the maker's word, not a fit we measured. Check the size below against your own.

PET bottlesFrom the maker's own listing tags, checked 2026-08-13. See the original post

Brand names here only say what this part fits. We are not connected to those companies, and they did not make or check this part.

What you get

This design prints as one piece.
Nothing else to print or buy for this to work.

What it is made of

Designs like this print well in PLA. Compare the materials.

Printed plastic is strong for its size, but it is not metal. We have not load tested this design, so we do not publish a weight rating. Keep it out of a hot car and away from open flame.