Boosted, I think you're confused. When Chris said his is a 76 trim, he IS talking about the turbine shaft. There is a compressor wheel trim, and a turbine wheel trim, as well as A/R ratios for the compressor and turbine housings. So there are a TON of combinations for turbo's.

But Chris is right, the turbine wheels are referred to in stages rather than sizes, to make it easier. I hate the whole "stage" thing because it sounds like ricers talking, but its common practice in the turbo world.