These collars can be used for various projects, a few I have thought of and undoubtedly many others that I just totally miss. When I first saw them I thought wine rack with 4 inch plastic pipe inside. Plant pot holders and pencil holders came to mind as well.
I did drill a hole in one to make sure it was easy to drill and seems to be good to go there.
Since new pipe is mostly plastic now these weld-on collars will gradually become extinct. They are somewhat heavy and shipping will be a fair amount of the cost. They weigh right at 1# 5 oz each. So putting a project together could get into some weight using several of them. The O.D. on the backside is 5" and I.D. on the front is 4". Height wise they are just shy of 3" tall.
All are rusty. Most if not all will have some dirt that the steel brush will remove. Some are cleaner than others but not by much.