Steve:
I bought some circle track wheels for my Z a few years back. They come with lug holes made for 45 degree lugs (like circle track racers use) I tried to find 12mm x 1.25 lugs with 45 degree taper and only could find aluminum ones. I thought in race conditions where the wheels are torqued and reomeved a lot it might be OK but got nervous and just used steel. So.... you use aluminum lugs on your car and no problems? torqueing tips? how often replace?