Wannabe, there are dozens of ASTM specifications for different kinds of steel plate. The cheapest/ cheeziest steel is A36 and is what most steel yards sell for plate. This steel machines easy, cuts easy, bends easy (threads tear out easy too :o )
For brake parts you want something that is tough yet has a high yield strength.
I provided the software and drive system for a local rolling mill plate shear and chopper, I was amazed at how many different grades of
steel they produced.
