This is an OEM Caliper Piston Kit used on the Rear Caliper of a 6th Generation ZL1 and ZL1 1LE. These are unique to that caliper are the exact OEM replacement. Please note that these are sold as an individual kit, one kit per caliper.
General Motors is an OEM manufacturer. GM designs and creates the vehicles and the parts for them for makes such as Buick, Cadillac, GMC, and Chevrolet. All GM branded parts are OEM standard quality components and were designed and manufactured to either be on the vehicle from the factory or purchased after the fact as an accessory.