Variations in the spring on the alarm sliders, no hole or hole at lower right.
Inner Shell Type Type 1:
Has leaf springs on alarm control levers attached at one end, outer end engages with inner ring on bezel. Used through March 1929.
Inner Shell Type Type 2:
Has spring between lever body and shell; no hole in shell at lower right. Used from March 1929 through late 1929 or early 1930.
Inner Shell Type Type 3:
Has spring between lever body and shell; has hole at lower right (where alarm pull switch is located on later models 1-L, 61-N and 61-R). Used starting late 1929 or early 1930.
