There were at least a couple more extended crossarms upon this bridge with "Pluto" insulators. This is an enlargement of an original photo (thanks, Jill McLaughlin!).

The "Pluto" insulators seen might have been used as fully reusable electric supply surplus in their day since these insulators have been found in elsewhere STL within the last couple years such as on a house service and during an excavation. A great many Pluto insulators also were used to carry electrical cables at the Chicago World Exhibition. There is some thought that these insulators and other electrical equipment used there was put onto the surplus market after the fair was closed and dismantled.

Aren't scenes visioning this kind of stuff as in this photo what your dreams sometimes look like?

Maybe the electrical contractor who installed LOTS of these for the Chicago Exposition wiring in the early 1890s reused them about ten years later for the St. Louis Expo...and then finally sold them off as cheap but fully resuable surplus insulators on the open market back thereafter? After all, it wasn't a throw-away society/world back then.

Added note: This line was removed long ago and according to collectors in the vicinity there hasn't been a trace of any Pluto insulators located anywhere near this installation.