Single cantilever on cap side
- Localized stress at one hook
- Harder to tune retention symmetrically
- Visible hook mark on one side
DFM
Annular Snap Fit: Injection Molding Design Rules
Annular snaps use hoop deflection for retention on caps and circular closures.
DFM
Annular snaps use radial deflection on a ring feature
Caps and closures often use annular snaps instead of single cantilever hooks.
Annular snaps rely on hoop deflection. Uniform wall around the snap ring matters.
Oval distortion from uneven wall thickness changes retention feel.
Degating and parting line placement on closures affect cosmetic cap surfaces.
DFM
Quote this rule with your CAD upload
NetProto DFM review flags these geometry patterns before steel is ordered.
- Call out draw direction and cosmetic faces on the model.
- Note resin family even when the grade is not final.
- Tighten tolerances only on mating features that need them.
Closure style
Single hook cap versus annular ring snap
Pick snap architecture before you lock cap aesthetics.
Annular snap ring
- Even retention around circumference when tuned
- Requires uniform wall and roundness control
- Tooling parting splits on cap geometry
Related rules
Design guide
Jump to sibling rules before you freeze CAD.
Design guide hub
All DFM topics on one route.
Design guide hubDFM article
Long form engineer guide.
DFM articleCantilever snap fit
Linear snap alternative.
Cantilever snap fitVenting
Air traps on cap geometry.
VentingPackaging industry page
Closure programs context.
Packaging industry pageVisual reference
Molding context for this rule
Images from the Forge media library illustrate typical programs.
Injection molded part design review on CAD
Injection molded part design review on CAD
Plastic housing with ribs and bosses
Plastic housing with ribs and bosses
Engineer measuring molded component
Engineer measuring molded component
FAQ
Annular snap questions
Do annular snaps need round parts?
Roundness and wall uniformity matter more than perfect CAD circles alone.
Can retention be adjusted after T1?
Minor steel safe changes possible. Large retention moves need redesign.
Are closures always PP?
Many caps use PP or PE families. State resin in RFQ.
Next step
Upload closure CAD for DFM
Cap and body models with snap section views help qualified quotes.