Another great song that popped in my head. You can see the trend in standardized sized tubes. The shapes may be ho hum but I like the markings. In this group the first 9 are marked with M, Macomb, and Triangle M for Illinois Porcelain Co. Don't know what was used on that long M marked tube but I tried all kinds of stuff and it won't come off. Must have been a sealant or glue. The last 4 are marked Thomas (R.Thomas & Sons Porcelain Co.) Dig that big Thomas wall tube. Must have been some huge wires that went through that thing!