SPI Mold Finish Standards

The SPI mold finish ratings allow you to specify a general mold surface finish.  The final part quality finish will vary with material and mold quality.

High Quality, Optical Quality
  • SPI Finish A-1 — Grade #3, 6000 Grit Diamond Buff
  • SPI Finish A-2 — Grade #6, 3000 Grit Diamond Buff
  • SPI Finish A-3 — Grade #15, 1200 Grit Diamond Buff
  • SPI Finish B-1 — 600 Grit Paper
  • SPI Finish B-2 — 400 Grit Paper
  • SPI Finish B-3 — 320 Grit Paper
Non-Cosmetic, Stone Polish
  • SPI Finish C-1 — 600 Grit Stone
  • SPI Finish C-2 — 400 Grit Stone
  • SPI Finish C-3 — 320 Grit Stone
Non-Cosmetic, Dry Blast, Matte Finish
  • SPI Finish D-1 — 600 Stone Prior to Dry Blast Glass Bead #11
  • SPI Finish D-2 — 400 Stone Prior to Dry Blast #240 Oxide
  • SPI Finish D-3 — 320 Stone Prior to Dry Blast #24 Oxide

Note that these are finish call outs for the mold itself and not the finished part.  The final part finish is a factor of the molding material and the mold steel.

Finish requirements can add to the mold cost and part costs.  Typically specify the lowest quality finish you can live with. 

Mold Textures

Mold textures are another method of calling out the finish for a molded part.  Textures can be photo-etched using patterns or chemically etched.  We will cover textures in a future post.