Here is a picture of some of the oldest Duquesne Light 23kv construction that I came across when I was in Pittsburgh. This particular line dates back to the 1920s and is outside Pitcairn PA. The insulators appear to be all Locke M-3155s but I also saw a lot of Lapp M-2702s and M-3348s on these old lines too. These older insulators are pretty rare on DLCo's 23kv system because most of them have been replaced with Lapp post insulators.