The SPI is that Society of the Plastics Industry  sets standard for plastics industry in the United States that identifies the cosmetic quality of plastics, Upmold uses  the SPI standard to define finish of plastic injection molded parts.
There are twelve grades of finishes specified by the SPI in four categories that range from shiny to dull. Each grade has different requirements for allowable deviation from perfect, with lower numbers allowing for less deviation and higher numbers allowing for more deviation.
Below specifications provide guidelines for mold surface finishes as provided by the UP MOLD.  For more information visit Tooling Manufacturing.

• SPI texture standard
• SPI mold finish standards
• Plastic surface finish chart
• SPI mold finish Guide
• Mold surface finish standards
• SPI Mold finish comparison 
• Injection mold  surface finish standards
• Injection molding surface finish
• Mold surface finish
• SPI surface finish specification
• SPI surface finish chart
• SPI surface finish standards

SPI a1 is comparable to RA.0-1 made by #3 diamond buff
SPI a2 is 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

SPI b1 is finer than a3 and RA.2-3 made by 600 grit
SPI b2 is slightly finer than b1 and RA.4-5 made by 400 grit
SPI b3 is comparable to RA.9-10 made by 320 grit

SPI c1 is finer than b3 and RA.10-12 made by 600 stone
SPI c2 is slightly finer than c1 and RA.25-28 made by 400 stone
SPI c3 is comparable to RA.38-42 made by 320 stone

SPI d1 is finer than c3 and RA.10-12 made by #11 glass bead sandblasting
SPI d2 is comparable to RA.26-32 made by 240 aluminum oxide sandblasting
SPI d3 is a little more coarse than d2 and RA.190-230 made by #24 aluminum oxide sandblasting

Shiny Finishes

SPI-A1, A2, A3

Semi-Gloss Finishes

SPI-B1, B2,B3

Matte to Dull

SPI-D1,D2,D3

Texture

SPI-D1,D2,D3