This model is said to be the second most common Vibroplex.  It allows for sending code more slowly than any other model.  It has a simplified "I" damper assembly and has no circuit closer.  It's frame and lever are like those of the Lightning.  Initially it came only in a black crackle base but that was changed to gray crackle in the Fifties.  Production stopped shortly after the company moved to Maine in 1979.