I doubt if strength was an issue in the engineer's design.
I will wager that the use of fine threads were called for to keep parts which you don't want to come loose, but are prone to.
I would bet that fine threaded fasteners were more expensive to procure, so GM must have had just cause to account for the additional cost.
1) the 2 bolts which hold the bottom of the radiator support to the front crossmember. The entire front of the truck body parts and radiator are kept in place by just these two bolts.
2) hinge bolts. Repetitive opening and closing of these heavy doors calls for a fastener less likely to back out.
3) the bolt-on crossmember which supports the torque tube ball and provides additional support to the frame in conjunction with the riveted-on engine mount crossmember. (In '54, GM eliminated the bolt-on crossmember when they redesigned a more robust engine support crossmember.)
On a side note, GM used fine threads behind the dash to hold the gauge cluster and speedometer on just to irritate me personally, given that it is nearly impossible to get to some of those. If I were ham-handed with sausage fingers, I would find another hobby just because of these fine threaded studs.
Carl
