these 3 insulators are attached to a house directly next door (to the west) of the first house ever built in the city of Lincoln, NE (the Kennard house). The Kennard house was built in 1869 or 1870. The house next door (with the insulators) was built in 1910. This area is almost smack dab in downtown Lincoln. see link:

http://www.nebraskahistory.org/sites/kennard/moreinfo.htm