Driveshaft uinv joint bolts?
 

Looks like the rear are a torx head and front hex head any reason for the two different bolts? Trying to figure out rear bolt head size

My bolts were hex head in the front and rear. I'm positive tht they are original. Not sure that domestic manufacturers were even using torx bolts 30 years ago.

I agree with 744544spd.
No torx bolts back in the late 60s early 70s.
My 68 driveshaft and half shafts have all hex head bolts.
Kurt

My 81 was the same way.

Geez...you guys come up with the most "off the wall" stuff...

I believe it was the late '70s/early '80s when GM went through their "METRIC" phase. They trained us all in metric measurements, told us how everything world-wide would go metric, started buying machinery that was built to metric specifications [and then used it to manufacture parts specified in "English" dimensions], and threw metric fasterners at the end-product to prove that we were converting. It wouldn't surprise me that there were some pretty weird assembly combinations in that time frame. [What a hoot to remember all that monkey-business!]

Same here:willy:

My 77 is hex front and rear, definitely original bolts.

...I thought the driveshaft bolts at the differential were a 1/4" 12 point bolt head design, not a Torx. I know the '80/'81 4spd cars with the steel spring had those Torx "E-10" size head bolts on the half shaft u-joints, but used those 1/4" 12 point ones on the differential u-joint.

...I also think it was 1978 where GM started using "some" metric fasteners-usually the head bolts were a light blue.:yesnod: