Molded internal thread
- Unscrewing or collapsible core adds mold cost
- Plastic threads strip under high torque
- Repairs often mean post mold machining or inserts
DFM
Molded In Threads: Injection Molding Design Rules
Molded threads remove inserts but add mold actions and torque limits.
DFM
Molded in threads trade assembly steps for mold complexity
Internal threads can eliminate inserts but need parting and unscrewing strategy.
Molded threads form directly in the cavity with rotating cores or collapsible cores on some tools.
Thread strength and wear differ from machined metal or brass inserts.
NetProto DFM review asks for thread class, engagement length, and resin before quoting thread tooling.
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.
Fastening
Molded thread versus insert or self tap boss
Pick the path that matches volume, torque, and rework tolerance.
Insert or self tapping boss
- Brass or helical inserts handle repeated assembly
- Boss design controls sink and retention
- Mold stays simpler without thread cores
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 articleBoss design
Boss geometry for fasteners.
Boss designSelf tapping screw bosses
Alternate fastening path.
Self tapping screw bossesInsert molding
NetProto insert programs.
Insert moldingVisual 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
Molded thread questions
Can any resin hold molded threads?
Tougher grades help, but torque spec still drives insert need.
Do molded threads need draft?
Helix is the feature. Parting and core pull still need a clear plan.
Who validates thread fit?
T1 samples and go no go checks on qualified programs.
Next step
Upload threaded features for DFM
Include thread class, engagement length, and assembly torque notes.