For use on Corvettes with the optional oil cooler (KC4). The KC4 option can be identified on the Corvette by where the oil filter screws into. If the oil filter screws into an oil cooler with an inlet and an outlet pipe which is then affixed to the engine block, you have the KC4 option. If the oil filter screws directly into the engine block, you do not have the KC4 option.
This is the upper molded 3/4" hose on the heater core. The 3/4" hose connects the heater core to the water pump fitting and branches to the 5/8" oil cooler pipe and the 5/16" small coolant vapor pipe. All fitments are correct to the original Corvette.