So the outside radius, my best attempt to draw it reasonably, the outside radius of the ring might look something like that. And the depth of the ring would be a little dy, just like that. So let me draw the depth. So let me see, right over here. You can kind of view it as the height of the ring because we are thinking in a vertical direction. So we have a ring for a given y, for say this y right over here. It's essentially the ring generated if you were to take this rectangle, this rectangle of height dy and rotate it around the line x equals 2.