It continued until the ring was so thin the lathe was removing metal from the tops of the screw heads and all the black anodized surface was gone. And then I went a tiny bit further but stopped short of totally removing the allen head sockets on the screw heads. If these had been eliminated it would have been very hard to remove the ring from the holding mount. Before I forget it the original screws were still available and untouched in terms of thickness. When the ring was re-attached to the lens these screw heads extended above the ring's top surface. They later were made to be flush with the top of the ring's surface using a Dremel tool with a grinding wheel attachment.