[Twoforty]

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[B]I've heard of lugbolts coming loose and becoming brittle with age -
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As a retired consultant metallurgist ( B. Sc. qualified) I would like to make the observation that techically steel does not become "brittle" with age.
Failure of wheel studs is however a common occurrence due to metal fatigue. This is caused by cyclic stresses exceeding the fatigue strength of the metal when stress concentrations such as thread roots are present.
Fatigue failures are avoided by installation at correct torque settings. ie. Avoid loose bolts.
Studs will last the life of the car if correct high tensile quality and sufficiently high installation torque.