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