These bangles were probably sold under the name "Marblette," and were designed to frame one or more sliced bangles (as shown in the first photo). Each one is rounded on one side and flat on the other. They are in very good condition with small age-appropriate signs of wear.
Each is about 3/8 inch wide, 1/4 inch thick, and has an opening of a hair over 2 1/2 inches.
The dark red bangle is not included.