Today’s project is small, useful and very satisfying: the Universal Bar Sealer, a 3D-printed bag clip that seals cereal, coffee, tea, chips and anything else that comes in a bag. It prints as one single piece, with a spring curled into one end and a snap latch at the other, so there are no metal parts to buy and nothing to assemble.
Why bother? Because the people who know coffee best agree that air, moisture, heat and light are what make it go stale. The National Coffee Association says opened whole beans stay at their best for only about 1 to 3 weeks at room temperature, and ground coffee for 1 to 2 weeks. A bag left gaping open on the counter loses that race fast. A firm clip is the simplest first line of defence.
What you’ll build
- Difficulty: easy. One part, no screws and no glue. It does need supports, and we explain why below.
- Sizes: 140 mm and 180 mm, with 110 mm and 153 mm of grip.
- Time: your slicer will give you the exact estimate for your printer.
- Cost: about 19 g or 26 g of PLA, depending on the size.
How it works
The clip has three working areas. At one end, a curled spring joins the base to the arm and keeps the clip open when you are not using it. Along the base, a centre rib and two side walls form two channels. The arm has two legs that drop into those channels when you close it, so the bag is pushed up and down in a zigzag instead of being pinched along one flat line.
At the other end is the snap latch: press the arm down and a small hook catches it with a click. The latch does the clamping, and the spring’s job is simply to open the clip again when you push the thumb tab outwards. A thin rib along the top of the arm stops it from bending as you press.
Our design in numbers
| Part | Shape | Key sizes |
|---|---|---|
| Base | Two channels, a centre rib and two side walls | 18.4 mm wide, 110 mm or 153 mm long |
| Spring | Curl at the end of the clip | About 2 mm thick, full clip width, opens 8° (140 mm) or 6° (180 mm) |
| Arm | Upside-down U with a rib on top | 11.7 mm wide, 2 mm thick |
| Latch | Hook with a thumb tab | 6.6 mm wide, on a flexible post |
We calculated the spring of the 140 mm size using typical figures for printed PLA. Closing the clip stresses the spring to about 17 MPa, roughly a third of PLA’s usual strength along the filament, and the spring pushes back with about 1.6 N at the tip, the weight of a 160 g object. These are calculations, not lab results, and your filament may behave a little differently. We also printed the 140 mm size and tested it, and it works as designed.
Materials and printer settings
- Material: PLA for the entire piece. Stiff and easy to print. Prusa’s material guide recommends around 215 °C for the first layer and 210 °C after, with a 60 °C bed. Keep PLA clips away from hot places such as a dishwasher or a sunny car: PLA softens at about 60 °C.
- Orientation: on its side. This is the important one. Lying on its side, the filament follows the curve of the spring, which is far stronger than stacking layers across it. Keep the engraved logo facing up.
- Supports: yes. The arm and the latch are narrower than the base, so on their side they start in mid-air. Use tree supports for those parts.
- Layers: 0.2 mm. Walls: 4 perimeters, so the 2 mm spring prints solid.
Step by step
- Download the size you need and open it in your slicer (PrusaSlicer, Bambu Studio, Cura and OrcaSlicer all work).
- Lay the clip on its side with the logo facing up, and turn on tree supports.
- Print it and remove the supports gently, especially around the latch.
- Test it without a bag: press the arm down until the latch clicks, then push the tab outwards. The clip should spring open by itself.
- Use it: squeeze the air out of the bag, slip the open clip over the top and press until it clicks.
Free STL download: Universal Bar Sealer 140 mm, Universal Bar Sealer 180 mm. Enter a valid email and we will send you the download link.
Troubleshooting
- The spring cracks: check that the clip was printed on its side, add a perimeter, or raise the nozzle temperature by 5 °C for better layer bonding.
- The latch is too stiff or won’t catch: clean any support marks from the hook, then file its tip a little at a time.
- The clip no longer opens fully: PLA can slowly take a set under constant load, more so in a warm place. It will still hold. Keep it away from heat, and leave it open when you are not using it.
- The clip warps at the ends: clean the print sheet and use a brim.
Safety and freshness notes
- Outside only. The clip touches the outside of the bag, not the food. Don’t use 3D prints as food containers or scoops: Prusa explains that layer lines can trap bacteria and are hard to clean, and that a standard brass nozzle is not considered food-safe.
- A clip is not a vault. It closes the bag firmly, but it is not truly airtight. For the best coffee, the National Coffee Association recommends an airtight, opaque container in a cool, dark cupboard, away from the oven and strong sunlight, and buying only what you will drink in one or two weeks.
Next steps
Once the clip works, make it yours: print it in your favourite colour, or add a hole so it can hang on a hook. If you enjoyed this one, our guide to making 3D models with AI tools shows how to sketch your own variations, and the course box below is a good place to learn proper 3D design from scratch.
Learn it by yourself, at your pace online
Want to go further? These online courses cover the skills behind this story:
- Introduction to 3D Design and Printing Domestika: Agustín Arroyo's beginner course: model an everyday object in Fusion 360, slice it in Cura and print it, no previous 3D experience needed.
See the course on Domestika
Read next
- How to make 3D models with ChatGPT and AI tools (2026 guide)
- Domestika courses for makers: 3D printing, Blender and more
- Arduino Ventuno Q: the board that gives robots eyes and a brain
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Sources
- Storage and shelf life – National Coffee Association USA (About Coffee), accessed 21 October 2026
- PLA – material guide – Prusa Research Knowledge Base, accessed 14 October 2026
- Food-safe prints – Prusa Research Knowledge Base, accessed 21 October 2026
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