I think the opposite. The heater core is 5/8 and 5/8 (restored by "the heaterboxguy" out of PA about 2 years ago) and he asked me what core sizes to use. Oops, I told him 5/8-5/8 not knowing my engine had the 5/8-1/2. Now it's time to pay the piper and deal with it. I was just asking if someone makes a rubber bushing or something. I'll either end up with 5/8 hose and the smaller orig Mopar ring clamp or 1/2 hose and get it hot and stretch it over the 5/8 core. Stupid little problems always getcha!!