Although the picture doesn't show this as clearly as it could, this shows the variation in the tops of CD 186.1 - the one on the left has two or three raised concentric rings on the top, while the one on the right is completely smooth. The top on the one on the right has some damage, so the red circle shows the area of the full top. Again, we have no idea of the function of these pieces, nor this significance of these different tops.