T o 4 means nothing to anybody.
That is the frame of the Compressor Housing....another words the outside dimension, and the use of a bearing carttridge, and T3 or T4 exhaust housing.
What turbo people want to know, and should know is this:
Compressor Inducer Measurement - taken by measuring the inlet hole...usually referred to in MM millimeters
Whether the Exhaust Housing is T3,T4, or T6 and what A/R choke the housing is...should be stamped something like .48, .68, .86, .98, 1.04
What the Exhaust Turbine Exducer measurement is - taken by measuring the exhaust outlet, and referred to in MM millimeters.
How much Up/Down shaft play there is...and how easily the wheel spins.
Thats it.
A picture of the turbo with a tape measure or a ruler usually over the blades is best. Its hard to Hide FOD damage with pics like that.