The shank is not exactly a precision piece of kit. All four sides measure slightly different..... It's basically 1/8" (0.125")
Pick some decent steel, especially if you plan to load it up, for example with ebikes or the +2 bike extension (total 4 bikes).

Depending on the vehicle the Thule threaded hitch draw bolt may prove to be too short.
Example, some of the 2023+ Toyota Sequoia models have a box around the hitch and require a longer bolt.
I hear some Subaru models too.
Rocky Mounts to the rescue. They sell a hitch draw bolt 15mm longer and intended for their own racks, but it's the same threading as my Thule T2 and worked for me.

Barry