Here is the pole top, with the CD 140.5 installed. I am now of the opinion that the CD 140.5 was designed to be a "heavy duty" insulator, for applications that needed to stand up to heavy strain. Note the pin has an extra thick diameter, with the threads starting just above a "shoulder" of greater diameter than the threads [id=348775670].

This shoulder perfectly mates with the surface around the threads inside the insulator [id=348775113], providing a very strong and secure mounting. It also explains the larger diameter compared to an EC&M (making room for the larger pin) and the extra thick heavy skirt of the CD 140.5 compared to an EC&M or California Electrical Works insulator. It is interesting to note that this pole had boards nailed to it like steps on a ladder... I guess someone was trying to make getting to the top of this pole easier... for ease of maintenance, perhaps?

I do not know the date of production of these insulators... so few of them have been found and the lines involved are difficult to identify or date. Any other insights or information from the collecting community is strongly encouraged! It would be nice to know if they are an EC&M or Cal. Elec. Wks. product.