Big Red Senior from 1928–9 I own several Duofold Seniors.
The specific one shown in this post was made in 1928 or 1929.
Not content to rest on the laurels of its successful Duofold line, Parker began to research alternatives to the sac sometime in the mid-to-late 1920s.
Elaborating on an invention by a University of Wisconsin engineer, Parker came up with an all-new filler system and installed it on a new and visually-arresting line of pens that first went on sale in 1932.
The Ring Top would also appear on Parker's Vest Pocket models, for being attached to a watch fob.