Early in my career at a dealership, I had taken a box of 5/16 coarse bolts to work cuz I had busted out of my flat rate twice cuz I had to stand in line at the parts counter waiting for 4 coarse thread bolts to replace the fine thread bolts I took out. Used a few outa that box thru the yrs.
Never forgot it, - on reflection, they may have been polys, they used the same pump.
But I do agree, after a few years, they were all coarse .