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Through Holes: Injection Molding Design Rules
Through holes open to the mold split on both ends, which changes venting and pin layout.
DFM
Through holes vent naturally when both ends reach the mold split
Open bores simplify fill and air escape compared with blind pockets.
Through holes often form with core pins spanning both mold halves at the parting line.
Pin alignment and flash control at the parting line matter for hole roundness.
Holes near thin walls need extra review so pins do not punch through during fill or ejection.
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.
Hole callouts
Through hole drawing notes
Send these with CAD for DFM sign off.
Hole diameter and tolerance band on mating features only
Position relative to datums or centerlines
Parting line location through the hole axis if not obvious
Cosmetic face near hole break edges
Related rules
Design guide
Jump to sibling rules before you freeze CAD.
DFM article
Long form engineer guide.
DFM articleBlind holes
Closed pocket rules.
Blind holesSide holes
Holes off pull direction.
Side holesStandard tolerances
Hole tolerance strategy.
Standard tolerancesVisual 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
Through hole questions
Can through holes be threaded?
See molded in threads and boss design for thread strategy.
Do through holes need draft?
Pin walls usually include draft for release unless using collapsible cores.
Can holes be angled to pull?
Angled holes may need side actions or parting splits.
Next step
Upload hole patterns on CAD
Include section views through critical bores before tooling.