On turbos there are a couple different numbers to know.
The compressor and turbine wheel sizes are most important, this determines the horsepower potential. Note that it is easy to over-buy on turbo size.
Ball bearing vs journal bearing, this determines how much torque converter stall speed is required to make the turbo spool.
The ".63" and ".55" on the outsides of the castings relate to the geometry of the castings, its known as A/R and comes into play when determining the operating pressure and flow range of the turbo. But there are small .63's and large .63's, so this is less of a key factor, especially concerning chips.
Note that a built engine shifts all the above around, so the key is to balance the build, components, and planned usage of the car.
With that out of the way, when ordering a chip your turbo is essentially a "journal bearing TE63".
Bob