As elite racing said earlier apparently the around 51 inches & over is the danger zone, which is about where the rwd skylines are, the loop is mainly to stop the shaft hitting the ground & potentially flipping the car
I’ll prob go back to 2 piece? , interesting on some of the later mustangs they’re going from the 2 piece to 1 after failures, there’s quite a lot of debate around it
(the 1 piece i have has upgraded unis, is around 2.75inches diameter & supposed to be good for over 10,000rpm? is about 50 inches long)