I'm looking at a cookbook, and it uses the term a tooth of garlic rather than clove. I don't think I've ever seen that term before.
It is "Some LIke it Hotter" by Geraldine Duncan who seems to have grown up in Southern California. The book was published around 1985.
@FF: Ha, ha! That's a fair guess! But it should be a teeth of garlic. But this one we say the same as you: a head of garlic = una cabeza de ajo. Which is equally nonsense because garlic has no tooth, nor mouth, nor head! Me myself, i have no head, go figure the garlic.