Disc brake rotor.

[ROD]

Are 'bike brake discs made of any special type of steel? Is it ok to use a disc made from stainless,say 6mm thick?   
         Thanks
 (for a parking brake ,not the main brakes)

[tbone]

Purely for a handbrake, to be applied when the vehicle has stopped, then i would say yes, you will get away with it.
Brake discs however are made from a variety of materials including cast iron and hardened steel with a high carbon content, to combat the heat generated from friction.
A mild steel compound would not withstand the heat or forces being applied to it.

[ROD]

OK thanx, I 'll use a 'bike one.The reason I asked was that all the bike ones seem to have existing holes of various sizes in the centre area,therefore difficult to find a concentric mounting place when bolting it to the diff flange.