[RICK LAKE]

N2Venon I didn't see the inside of the spinner but the spindle threads are stripped. I have 3 thoughts on this failure
The spinners where not retighten after every run. You have a heat cycle, metals expand and retract. This is the reason safety checks are done at events. I think if you pulled on the wheel top and bottom you would have gotten a rock motion. Just because you have safety wire in the spinner doesn't mean that the spinner doesn't loosen. It's not a sure thing
Is it possible that the spinner is not stainless or weak aluminum? The hub could also be the same thing.
Gald car was not heavily damaged and you where going 120+ mph.
If you are going to stay with spinner, I have found that with a 4 pound plastic dead blow hammer you can tighen up spinners after every run when things are hot. I am a little surprised that the car was not funny in the rearend before breaking. Either a wobble, small vibration, should have felt it in your butt. I know guys who run nuts for there wheels and have 500ft of torque on the nuts and safety clips.
Any time you have the cobra on a jack, check the front and rear tires for play. this could be loose wheel bearings, loose spinners, rear hub housing bearings or end play too much. tierod ends, inner or outters. Rick L.