A fishtail nose stud has nothing to do with the tail of a fish. It consists, in all its simplicity, of a straight metal bar with a head. We can't call it ball because a spike cannot be categorized as a ball. In this case, you can choose between a ball, a spike, and a hemisphere or a half ball. The spike and the hemisphere are flat at the back, i.e., they will lay flat on your nose if that's how you choose your jewelry. You can also use this stud elsewhere in the body. For example, you can custom-make it for your ear, where one is usually pierced with a 20g (0.8 mm) or an 18g (1 mm) needle. 

With this fishtail stud, you will also decide the length of your bar. It's 3/4" (19 mm) long by default, so you can flex and bend it with the right tool to suit your piercing.