This is a brand new OEM GM rear carbon ceramic 2 piece light weight rotor, which are sold individually. It fits the 2009 to 2013 Chevy Corvette ZR1 with the Brembo brakes.
GM OEM part # 84488400
AC Delco part # 177-1256
Don't confuse this with some people selling cast steel rotors and using the same part number and selling them for less. They weigh more than 2x what these weigh and do not perform the same.
This rotor weighs about 16 pounds. A steel rotor of this size would weigh over 30 to 40 pounds.
Your local GM dealer will charge you about $1600 to $1800 each for these.