You know, I’m embarrassed to say this…but in 23 years of designing plastic products, I’ve never had to put on a drawing a definition of a polish level. I’ve always just handed a sample to the toolmaker and said replicate this, or gave it a subjective definition of “high polish” or “mirror finish”.
So, I have no clue what SPI definitions relate to a surface finish of something like a Lego Brick.
Google hasn’t come up, quickly, with a layman’s example of polish definitions.
That is one of the links I found when Googling about. It gives quantitative descriptions based on grit and materials used, but there is no real world comparison.
Ironically, from the descriptions, I was assuming SPI A3 was what was used for Lego blocks as well.
The mold-tech catalog I use does not have different glossy finishes. It’s more for textures and varying degrees of matte. Not sure if there’s a bigger MT catalog available, though. I think the one we had was like $400-500.
Probably A3, usually when doing high polish you only go higher when it is a part with optical properties.
A3 finishes are more usually resistant to scratches as well compared to an A1. A1 parts are so smooth that even the slightest abrasion during handling or use will quickly scuff the surface of your plastic.