Sometimes in the course of restoring a very old luminaire it becomes necessary to recreate components. These are spinnings used to cover the lower mounting assembly. The one on the bottom left was at some point used as a replacement part. Can you tell which one is the brand new replication part?
Top! You can tell because the one on the bottom right, the original, was slotted at the pipe hole. With more modern technology we can make a pretty perfect fit without having to slot the spinning.