I'm betting it has to do with the fact that the shaft is also load bearing since there isn't an upper control arm. I don't know anyone that has broken a stub axle/spindle on a C2/3/4 vette and they all used the same style.
Hopefully the new beefy axle works.
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Trey
Current ride: 2001 BMW 540iT soon to be manual swapped.
Former rides: 1979 Trans Am WS6: LT1/T56, Kore 3 C5/6 brakes, BMW 18in rims