That's an odd combination. I'm not used to seeing disks with duplexes or triplexes. Probably leftover disks from the lines that were taken down?

Possible. The first time I saw this it was built like a 2400V singlephase line, strongly suggesting that there was once a 6.6A series lighting loop in use here, and the discs would have provided the needed 'break' for connecting a light.

These lights are like the LED equivalent of the open bottom refracter type lamps. I have one of these on the pole in front of my house. I like them because for an LED type light they are actually the closest mockup of original mercury and hps construction unlike some of the other odd LED street lights that exist.