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Self Tapping Screw Bosses: Injection Molding Design Rules
Self tap bosses need pilot geometry and wall support, not just a thick cylinder.
DFM
Self tapping screw bosses need wall support and pilot geometry
The screw cuts its own thread in plastic. Boss design sets strip and crack risk.
Pilot diameter and depth control how much plastic the screw displaces.
Bosses isolated on thin walls sink or crack before the screw ever strips.
Glass filled resins are harder on bosses than unfilled grades in the same geometry.
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.
Boss drawing
Self tap boss inputs for DFM
Send these with CAD before mold steel is cut.
Screw size and vendor spec sheet if selected
Boss OD, pilot depth, and connection to wall or rib
Cosmetic face opposite thick boss roots
Expected assembly cycles or torque class
Related rules
Design guide
Jump to sibling rules before you freeze CAD.
DFM article
Long form engineer guide.
DFM articleBoss design
Core bosses and sink control.
Boss designMolded in inserts
When inserts beat self tap.
Molded in insertsRib design
Tie bosses to structure.
Rib designVisual 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
Self tap boss questions
Can bosses be molded without inserts?
Yes when boss geometry and resin match the screw vendor guidance.
Do self tap bosses need draft?
Outer boss walls follow normal draft rules for release.
What if the boss cracks in assembly?
Usually pilot, wall thickness, or resin choice. Review on T1.
Next step
Quote bosses with screw spec
Upload boss sections and fastener data with your CAD.