This insulator was invented around 1917 by Henry M. Byllesby (formerly of Edison, Westinghouse, and T.H.E. Co.), who formed his own engineering company (H. M. Byllesby & Company) in Chicago. "The insulator consists of a micarta core on which are assembled glass disks separated by asbestos washers and held in place by a simple interlocking washer and cotter key. After the parts are in place the unit is heated uniformly to a temperature of 100 deg. Fahr. and [tar] compound poured into the core through the top casting" (Electrical World, April 21, 1917) It's reported that 15,000 of these units were made, although they are very rare today, with only 2 purple strings and perhaps 3 original aqua strings known. The purple unit pictured sold on eBay in June, 2010 for $20,000. The aqua shells were aparently produced by Hemingray (shell fragments were found at the company dump), but the maker of the purple shells is unknown, possibly the same glasshouse that made the Cochrane bells. Two sizes were made, one with 5 disks (pictured), and other with 11. "The eleven-disk insulators will be used exclusively on the 110,000-volt line which is being built from Wisconsin to Minneapolis to serve the Twin Cities. The line west of Stillwater is being requipped with them. Five disk insulators are being placed on a number of 60,000-volt lines in various parts of Minnesota. The Montana Power Company was one of the first companies to try out the glass disk feature." (ibid) The five disc units were also used in California.

Patented by Harry Hamilton Cochrane of Butte, Montana in 1916 (No. 1,194,957), these "Cochrane Bells" were used only in Montana, mostly on the 65KV, 13½-mile Cochrane line which ran from the Bertha substation near Corbin to the Porphry Dike mine. The shells are stacked on a parafin-soaked oak rod with cork washers between; cast iron caps screwed to either end of the threaded rod clamped the assembly together. The shells come in purple shades from near-clear to a rich full purple; pictured is the typical medium purple. A much rarer stationary version with ten larger bells also exists.