I say the device pictured by Bill Horne is half of a paired Fiber Optic Storage Loop. See:
When fiber optic cable is installed on poles, sections are chosen to be "too long" in case extra length is required later to accommodate splices, additional equipment and relocations of poles. The carrier wants to minimize the chances of having to cut and re-splice the many individual fibers within each cable, which takes substantial labor and causes service outages.
Fifty feet or more of fiber is tripled back upon itself between two poles to "store" that length for future use. The loop devices are made of painted metal. I suppose they could be spring-loaded to compensate for expansion and contraction, although I have not seen that feature mentioned in web sources.
The 15- to 20-inch diameter of these devices assures that the fiber is never bent smaller than its minimum radius which will either degrade data performance or will crack the fiber strands, making them useless.
Greg Monti snipped-for-privacy@mindspring.com