On the left is the Hemingray CD 152 [085] "Brookfield Style" mold, on the right is the CD 157 "teepee", and in the middle is the CD 169 Type I.

So why are these three grouped together? As you can see, all three styles are very similar from the wire groove up. Following the recent ICON discussion on the Type I, these three styles were among those tested in a c.1910 experiment by AT&T to come up with a new standard insulator. It appears that the CD 152 was the eventual outcome, but the CD 157 was also produced as well. The Type I prototype wasn't so lucky; there are only about 4 or 5 known to the hobby.

For more information on the experiment, please read David Wiecek's article at http://www.insulators.info/articles/attarc.htm