Annular snap-fit

A beaded plug and a grooved ring — the round snap joint.

The annular snap is the round sibling of the cantilever snap. A post carries a raised bead near its tip; the receiving ring has a narrower bore and an internal groove. Pushing the post through the bore deflects the bead until it springs into the groove and is retained — the joint used for pen caps, bottle caps, and round enclosures. Retention is purely geometric: the bore is narrower than the bead so it can’t pull back out, and the bead protrusion must exceed the clearance gap or nothing would hold. Both parts are laid out to print flat.

1. Set the post radius and height, the bead protrusion and thickness, and the snap gap.
2. Set the ring wall thickness (leave the ring on to get the receiving part too).
3. Generate: the plug and ring drop in side by side as editable parts.