Impossible Reuleaux Triangle Bolt with Square Nut & Clicker Mechanism
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Fidget Reuleaux triangle-shaped bolt with a smoothly threading square nut and a satisfying clicker mechanism
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Updated at source:
Model information
- Source
- Printables
- Category
- Other Toys & Games
- License
- Creative Commons — Attribution — Share Alike
Why does an elephant have round legs? It’s so that it doesn’t fall through square holes!
The bolt is shaped like a Reuleaux triangle, allowing a square nut to thread smoothly around it — an impossible-seeming interaction made real by geometry. A second, a round nut is included, but with a larger diameter.
I recommend printing with 0.15mm layer height with PLA. A 0.20mm layer height might works but could require more effort when threading or break along the layer lines.
Clearance testing
Ensure your printer is well-tuned — ideally capable of printing functional M6 threads. To test clearances before printing the full bolt:
- Print the end cap and retainer disc.
- Default thread clearance is 0.1mm inner/outer.
- If threading is too tight, try larger inner clearances (0.2mm or 0.3mm).
- If still tight, scale parts with inner threads in X and Y in slicer
If you experience clearance issues with round or square nut try scaling them by a factor of 1.05-1.10 in X and Y axes.
Assembling
- Start by screwing the end cap and the ratchet wheel.
- Put the clicking ring on the ratchet wheel; a slight rotation can help it click into place.
- Screw on the retainer disc.
- Now screw the round nut and the square nut on the bolt.
- Now you can screw the clicker head and the bolt together.
Model in onshape: link.