In the early 70's cars were being built with catalytic converters, which necessitated the use of unleaded gasoline because leaded gas would coat the catalytic m

In the early 70's cars were being built with catalytic converters, which necessitated the use of unleaded gasoline because leaded gas would coat the catalytic material in the converter and ruin it. Cars designed to use unleaded gas would have a fuel filler with a smaller hole in it, and unleaded pumps would have a nozzle that fit in the hole, while leaded and diesel nozzles wouldn't.