SPI Surface Finish Chart for Roughness Technology
Grade A
SPI a1: comparable to RA.0-1 made by #3 diamond buff
SPI a2: slightly finer than a1 and RA.1-2 made by #6 diamond buff
SPI a3: has more imperfections than a2 and RA.2-3 made by #15 diamond buff
Grade B
SPI b1: finer than a3 and RA.2-3 made by 600 grit
SPI b2: slightly finer than b1 and RA.4-5 made by 400 grit
SPI b3: comparable to RA.9-10 made by 320 grit
Grade C
SPI c1: finer than b3 and RA.10-12 made by 600 stone
SPI c2: slightly finer than c1 and RA.25-28 made by 400 stone
SPI c3: comparable to RA.38-42 made by 320 stone
Grade D
SPI d1: finer than c3 and RA.10-12 made by #11 glass bead sandblasting
SPI d2: comparable to RA.26-32 made by 240 aluminum oxide sandblasting
SPI d3: a little more coarse than d2 and RA.190-230 made by #24 aluminum oxide sandblasting
12 grades · one clear specification
Stop Guessing at Mold Finish: Choose the Right SPI Grade
“Glossy” and “matte” mean different things to different suppliers. Use the SPI mold finish chart below to put a grade, finishing method and typical Ra range on the drawing—before tooling, sampling or approval.
| SPI grade | Finishing method | Surface roughness Ra (μm) | Finish look |
|---|---|---|---|
| SPI A1 | 6000 Grit Diamond | 0.012–0.025 | Super High Glossy |
| SPI A2 | 3000 Grit Diamond | 0.012–0.025 | High Glossy |
| SPI A3 | 1200 Grit Diamond | 0.05–0.10 | Normal Glossy |
| SPI B1 | 600 Grit Paper | 0.05–0.10 | Fine Semi-glossy |
| SPI B2 | 400 Grit Paper | 0.10–0.15 | Medium Semi-glossy |
| SPI B3 | 320 Grit Paper | 0.28–0.32 | Normal Semi-glossy |
| SPI C1 | 600 Grit Stone | 0.35–0.40 | Fine Matte |
| SPI C2 | 400 Grit Stone | 0.45–0.55 | Medium Matte |
| SPI C3 | 320 Grit Stone | 0.63–0.70 | Normal Matte |
| SPI D1 | Dry Blast Glass Bead | 0.80–1.00 | Satin Textured |
| SPI D2 | Dry Blast | 1.00–2.80 | Dull Textured |
| SPI D3 | Dry Blast | 3.20–18.0 | Rough Textured |
Practical note: Ra values are typical reference ranges. Resin, color, wall thickness, draft angle and molding conditions can change the final visual result. Approve a physical sample or finish plaque before production.