N. R. "Woody" Woodward is the author of The Glass Insulator in America, 1988 Report and developed the Consolidated Design Numbers identification system for glass insulators. 

QUESTION: Is the smaller Pyrex CD 128 type piece embossed: (F-Skirt) PYREX/REG. U.S.PAT. OFF the rare CD 111 Pyrex? It is much shorter than the CD 128 style.

Comparison scale drawings of CD 111 (left) and CD 128 (right). Scale drawings of each CD are available in Woodward's THE GLASS INSULATOR IN AMERICA, 1988 Report. (See Reference Library page 58 in this issue)

As is the case with several CDs, the CD 128 does cover a wide range of shapes. The insulator (on the left on the previous page) is, I believe, the very first CD 128 in the Corning line (and therefore, the first since Corning was the only one to make that CD for many years). I had seen one of those before. [Insulator on the right is a later and variety with the more standard dimensions.] 

The insulator on the left is not the CD 111, although the embossing is identical and I suspect they were made at about the same time. CD 111, although height and base diameter are about the same as your sample, is more slender, the wire groove is narrower, as is its crown diameter. The body is not nearly so heavy. 

Insofar as I know, at this time the only known CD 111 is in the museum at Lyons, Colorado, where it was donated by Al Campbell's widow some years ago. The time I first saw that particular insulator, some 30 years ago, I was not aware of the other early Pyrex pieces that are in between the CD 111 and the later, more familiar ones. Had I been, I probably would not have assigned a new number. But since it has been assigned and illustrated in print, best to leave it that way. 

There is really a great variety in Pyrex CD 128, we have at least two variations of these very early ones with the very thick skirt and slanting sides. Then when they went into mass production with the B series, the design was changed and again with the E series. The N series has the very short spiral of inner threads in the skirt. Series O through S are a bit different again, then inner skirt ridges were dropped and we have those extra wide styles (2-3/4" base diameter). Then finally the last of the line, the 1941 production CSA that is an exact duplicate of the Hemingray.