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rodhusk
Eseman
That’s the inner diameter of the top - bottom bearing, respectively.
There’s a few different type of threadless headsets (which that bike would have): integrated, zero stack and external. I can’t tell from the pic if yours is integrated or semi-integrated/zero stack.
In reverse order...
External headsets have cups that are pressed into the headtube, and they sit the bearings beyond the lip of the headtube. These are older tech and can have loose ball bearings or bearing cartridges.
Semi-Integrated headsets also have cups that are pressed into the headtube, but they situate the bearings inside of the headtube. Instead of the whole cup, only a small lip protrudes beyond the headtube. They usually use bearing cartridges.
Integrated headsets have the headset ‘cup’ built into the headtube. This headset only uses cartridge bearings, without any cup being pressed into the headtube.
35/45 deg refer to the angle of the contact surfaces of the cartridge bearing. It’s important to get the right angle or you’ll wear/damage your kit.