Anthony;c-146078 wrote240s and previous models are imperial threads as mentioned above, so why is this so, from a metric country.
Answer is starting with the driveline of two section tailshafts, uni joints, differential and axles, wheel studs, limited slip centres, 99% is imperial as Volvo licensed this ultra strong driveline design from the US Dana-Spicer (Dana Corporation).
1975 was the change over year from imperial to metric on Volvo's, coinciding with the introduction of the 200 series cars. Up to and including 1974, most fasteners were UNC threads, with UNF threads for a handful of things, as you've listed above.
It seems that they decided to keep UNF threads in a few locations, my theory is that going to comparable strength metric fine thread bolts would have added no advantage, so they avoided the tooling cost, and also the suppliers of driveline parts like diffs, axles and uni joints were mostly Dana (USA) and GKN (UK) who's products used imperial threads as standard.
Note also that seatbelt mounting bolts also all remained UNF until at least the end of the 200 and 700 series, and probably later.