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Glossary

What Is an SPI C1 Finish? Injection Molding Explained

SPI C1 is a matte stone polish band on the SPI finish chart.

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Glossary

SPI C1 is a fine stone finish that reads matte on the part

C grades hide minor flow witness better than polished A or B surfaces.

C1 uses stone polish steps that leave a uniform matte microtexture on cavity steel.

It suits interior faces and low glare exteriors when gloss is not desired.

Draft and ejection still matter on C1 faces because texture increases pull.

Glossary

How spi c1 finish shows up on real programs

Library photos illustrate molding and tooling context for this term.

  • Use the term in RFQs with geometry and material context, not in isolation.
  • Link to the design guide when the term affects steel or part design.
  • Upload CAD when the term changes tooling scope or piece price.
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Engineer reviewing injection molding terminology on a part drawing

Appearance

Polished B grade versus stone C1

Pick based on glare and defect visibility, not only cost.

SPI B1 visible housing

  • Shows gloss and can highlight flow marks
  • Fingerprints visible in use

SPI C1 same geometry

  • Matte look hides minor flow witness
  • Texture increases pull so draft matters

Go deeper

Where this term connects

Each link is a different angle on the same program, not a duplicate definition.

Visual reference

Photos from molding and tooling programs

Images are selected from the NetProto Forge media library for this topic.

Injection molded production parts on a tray

Injection molded production parts on a tray

Injection molded production parts on a tray

Engineer reviewing a molded part drawing

Engineer reviewing a molded part drawing

Engineer reviewing a molded part drawing

Plastic housing components from a steel tool

Plastic housing components from a steel tool

Plastic housing components from a steel tool

FAQ

SPI C1 questions

How does C1 relate to MoldTech?

SPI is polish level. MoldTech is etched grain from plaques.

Can C1 face meet A2 face?

Yes with steel shutoffs when the drawing defines both.

Does C1 need less mold maintenance?

Matte can hide minor scratches but wear still occurs at gates.

Next step

Call out matte faces on CAD

Upload models with SPI bands per face before texture work.

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