Legal wear on drums?

[J&E <ebk@buffnet.net>]

Hello List again!
        Another question popped into my head reguarding AL. Fin Rear Brake
Drums. I have learned that the AL Fin Drum has a steel lining inside the
drum. Which makes sense. My question is: if one is to obtain a used set
of AL Fin Drums, then how does one know if the are reusable? or If
turned down beyond "safety" spects? I shall post any "off line"
responces back to the TR List. TIA -Cosmo Kramer