These days, you don't have to be a skater to know that skateboards are definitively "cool"—all you need to do is check your local fashion campaign or designer department store for proof. But boards are for riding, not wearing, and having one means learning your way around its components. If you don't know where to start, here's your first lesson: a skateboard is the sum of its parts. To that end, we break down the math to make sure everything adds up before you buy one. From decks to bearings, here's a crib sheet of the different elements of a skateboard—and who's making them the best.