Compatible with Ball Jars: Fermentation Cap with Water Seal

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The maker says it fits: Ball Canning Jar. See the proof

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What it does

Water-seal design lets CO2 escape while blocking air to prevent spoilage
Fits classic Ball canning jars with glass lids and wire bails
Ideal for small-batch vegetable fermentation experiments
Cap sits above food, no direct contact with fermenting ingredients
Printable with adjustable parameters for custom sizing

This fermentation cap transforms standard Ball canning jars into small-batch fermentation vessels. Designed for home fermenters exploring live-culture vegetables, it features a water-filled moat that allows carbon dioxide to escape while preventing oxygen from spoiling your batch.

The cap fits over classic Ball jars with glass tops and wire bail closures. Fill the moat channel with water, place your jar lid, then seat the cap on top to create an airlock seal. Because the cap rests above the jar opening, it never touches your fermenting food.

Originally created for a fermentation workshop focusing on raw vegetable cultures, this design includes adjustable parameters so you can fine-tune the fit for your specific jars. Print with settings that ensure watertight walls and bottom for proper sealing.

Not affiliated with, endorsed by, or sponsored by Ball. Ball and its product names are trademarks of their respective owners.

2.6k 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: Ball Canning Jar

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

Ball Canning JarFrom the maker's own listing title, 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 PETG. 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 We have not load tested this design, so we do not publish a weight rating.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.