I use grade 8 bolts and steel lock nuts on the rear, no nylocks the heat softens the plastic
I use grade 8 studs with a 12pt grade 8 nut on the coupler. Then I can use a 3/8 box end wrench to tighten the driveshaft to the coupler. The 1/2 head is too big to get anything but and opened on and they never really get tight.
When roadracing, with the constant shifting as well as going from 120+mph to 35 for 35+ minutes at a time, the driveshaft must stay tight and this system has worked flawlessly.
I used the studs & nuts for the very first time when I competed in a 25 hour endurance race back in 2003 and they performed without any problem.
You can see the studs & nuts here;
www.RPMracingCa.comRandy - RPM