Here's some other solid spools for these brackets that I have. So far there are only two companies that I have marked that made these spools. The first spool in the picture is marked with a Illinoise state outline/ ILLINOIS/1939. The second spool is marked with a U in a circle (Universal Clay Products) and 5012-2 on the other side. The other two are unmarked as well as the ones I have on the bracket. Surely there must be a patent or something explaning the use and manufacture of these neat pieces. So far none of the catalogs I have looked at from different companies show this type of spool.