This Graphic is extracted and reconstructed/colored/annotated from a partial drawing included in H. Morgan Brookfield's April 10, 1900 patent for an automatic press that had self-opening and closing four piece molds.
Two insulators (patent says adaptable to other objects), specifically CD 102s (or maybe 126 SKEBs?) are shown in the patent as being made in this four piece mold.
The mold's four pieces were: 1. Base with side-by-side depressions (D1 and D2) where the insulator dome would be formed. 2. The back "wall" which had two cavities in it for making the R-skirts of the insulators. 3. The front saloon door-style mold cheeks which each had a cavity for forming the F-Skirts of the insulators.
The mold closed by itself - actuated by cams on the rotating table it was mounted on. Glass was dropped into the mold. Parallel "actuating rods," each having a screw plunger for a tip, were pushed into the mold to press the insulators. After a couple more steps the mold auto-opened so an operator could remove the insulators.
This patent was applied for on May 7, 1898 and is US patent 646948