If you look on the website or call the company from which the turbo came they will state exactly what spec each stage turbo they do is
If you dont know then ask the person your bought it from, as you say it's new.

Rule of thumb for RST T3's IME is...

Stock T3 .36 Turbine housing .42 Compressor
Stage 1 As above with 360 degree thrust bearing.
Stage 2 As above with a .55 Compressor.
Stage 3 As above with .48 Turbine housing.