SPI Finish Grades:

• A1 Mirror: Ra 0.012-0.025μm — optical parts
• A2 High Gloss: Ra 0.025-0.05μm
• B1 Fine: Ra 0.05-0.1μm — general appearance
• C1 EDM: Ra 1.6-3.2μm — textured surfaces
• D1 Sandblast: Ra 3.2-6.3μm

Cost: Mirror finish costs 5-10x more than EDM finish.

Full guide: https://www.mfgabc.com/guides/surface-finish-standards-ra-rz.html

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