Almost lost a wheel

I'm using modern billet adapters on my SBP drums to run BBP wheels. Car developed a vibration and this is what I found on left front. 3 of the 5 lug studs had sheared off. Nuts on sheared lugs do no appear to have backed off prior to failing. Because I could not buy LH thread lug nuts with the larger conical seat I used the stock nuts to hold the adapter on. Was my error in not using the large conical nuts, or failing to use lock tite on the stock nuts I used, or improper torque on nuts holding spacer to drum. Any similiar experiences ? Opinions ?

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