Threadless flatbacks have custom fit posts where you choose the size that best fits the thickness of your ear. When piercing we do need to pierce with a longer back to accommodate for any swelling during the healing process but when the piercing is healed you can return for us to downsize the post length. One of the biggest differences aside from being able to choose the length is that the backing post goes in first and then you snap the head on. See the photo provided for how the head snaps into the post.