I don't expect you Whipper Snappers to know this but back in the Early 1980's it was the rage to tape a pair of Cow Magnets to your fuel line and it was reported it would improve your cars mileage.
The magnets are about 1 inch wide and 3 inches long and the farmer forces one down into one of the cows stomachs where it will catch any metal that is in the feed a cow eats and reduce injury to that Holstein worth a couple of thousand dollars.
I tried them on both of our vehicles for a friend in the repair business to test them. There was zero difference but he had customers swearing to him that they were miracle so he bought a case of them and charged big bucks to these believers and had them sign a disclaimer he had drawn up...