If you look into an atty, you will see a metal mesh curved loop sticking up. that is the bridge. It is designed to wick
juice from a cart to the coil, which is under the bridge (its like a little toaster coil, and you can see it glow in a clean atty on either side of the bridge. Some like to just drip, however, and not use carts, and they prefer the bridge to be gone, so the coil is fully exposed. You can
buy them from a few vendors, but most people remove them themselves. Have to be very careful and gingerly, as it is easy to break the coil.