SPI Specs

The U.S. Society of the Plastics Industry (SPI) coded a series of steel tool finishes, noting as well the steps to achieve it. Following is the resulting list, that is regarded as a reference standard by most in the industry in the US.

A-1 (Grade #3 Diamond Buff)
A-2 (Grade #6 Diamond Buff)
A-3 (Grade #15 Diamond Buff)

B-1 (600 Grit Paper)
B-2 (400 Grit Paper)
B-3 (320 Grit Paper)

C-1 (600 Stone)
C-2 (400 Stone)
C-3 (320 Stone)

D-1 (Dry Blast Glass Bead #11)
D-2 (Dry Blast #240 Oxide)
D-3 (Dry Blast #24 Oxide) finishes.