Here's one collector's idea about the purpose of those screw tops on CD 158.9's. Bill Pottichen writes, "I feel that some sort of wrench made of wood could thread the insulator onto a threadless pin.

"But one would need some sort of pressure from the top. Answer, a piece of hard wood with a hole in the middle of it. This hole would have threads inside. With left-handed threads on the tops, screwing the insulator down would form threads on a threadless pin."

Bill's idea coincides with that of many collectors that the CD 158.9's were sold by Boston Bottle Works as replacement upgrades for threadless insulators. On the opposite page is a sketch Bill submitted to illustrate his point. According to the theory, the segmented glass threads inside the Boston CD 158.9 insulator would cut its own threads on the wood threadless pin.

In an 1870's era advertisement for insulators made by Boston Bottle Works, supply Partick & Carter proclaimed, "...the 'Patent Sectional Thread Insulator' is considered far superior to any other forms of Screw Glass Insulator now in use. The following are some of the advantages claimed for this Insulator over all others: 1st It will cut its own thread upon a plain pin or bracket...". (See page 27 of the June 2004 issue of Crown Jewels magazine.)

The insulator shown with the advertisement was a CD 158 with a six-sided dome. It is speculated that some type of wrench would fit over the dome of this style of insulator also when screwing it in place on a previously threadless pin.

The concept had potential advertising appeal, as companies converting over to the superior threaded insulators would only have to replace the insulator, and not the pin, too.

So far we are not aware of anyone finding an actual tool used for screwing down Boston insulators.

Bill Pottichen's concept for how a "screw top" Boston worked.