HI...Found this info on the FOHBC website...authored by Dave Hinson...
"The Atlas E-Z Seal and Atlas Strong Shoulder jars: The Atlas E-Z Seal is a variation of the Lightning seal jar already described. The "Strong Shoulder" jar is a variation of the old shoulder seal mason jar. However, this jar sealed on a raised lip to help keep the jar from cracking - a common problem with shoulder seal jars. This concept led to the term "Strong Shoulder" as used by the Atlas company for their jars. The Hazel-Atlas Glass Company, makers of the E-Z Seal and Strong Shoulder jars, was in business from the late 1800s until 1964. These two jars date from the 1920s. The Hazel-Atlas company specialized in producing fruit jars."