Where did you learn that they are chrome-plated? For some reason, I had thought that they were nickel plated.
Also, My first thought for OD was "optical density", as with safety goggles. Which I would guess depends on direction-longitudinally/out the front, the OD would be extremely low; but transverse/from the side, I would say the OD would be extremely high. Outer diameter makes MUCH more sense.
Would .003" gap be too much? would it still make good thermal contact?
I kind of like the idea of under sizing the bore, than just sanding it to a fit. But when doing it by hand, it’s hard to keep the hole from becoming elongated.
How ridged are the Aixiz housing? Do you think they could withstand being pressed into a .002" undersized hole? The heat sink is only aluminum, and the housing is brass, so the heat sink would be softer, plus there would be thermal grease all over it which would help keep friction to a minimum. And their only $5, so if I screw one up its not a big deal.