These are the wiring harness mounting rails that were originally used on the 1967-1972 Chevrolet and GMC trucks. It is used to clean up under the hood and protect the wiring. This is a two piece set with one mounting to the firewall and the other to the radiator core support to contain the wiring and keep it up and away from the engine. These rails can be used on all years to clean up the engine compartment.