I do not have a better reference for this at the moment, other than it came from a technical journal/book published in 1906... You will see in the upper left... No doubt CD 286.9 !! If it's not threaded, but has the bumps as the specimen we have today, it was cemented on the pin.

Clearly shows it as a "pin type" insulator, I would say! If you had to put it in the threaded or threadless camp, I would be inclined to put it in the threaded camp, because of the precedent with the foreign pieces with bumps and ridged, etc. in the pin hole to add surface area for the cement to grip.

I consider threadless as having a true smooth interior.

In any case, enjoy the photo! There are some other goodies around... some I wasn't able to fit on this page. I'll try and post the rest so you can see everything.

Sorry about the quality, it's picking up all the dots from the printing...