If you are drag racing use chromoly for the cage and mild for the baseplates. If your car is for roadrace or drifting mild steel would probably be a better choice since the metal is far less brittle especially at the weld joints.
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Don't bother giving me "rep", I won't return it and I think it is stupid.
Gracie Barra Clearwater
Gyms in Clearwater, St. Pete and Port Richey
pm me if you are interested in trying a free class at any of the gyms.