They look like inserts that are used to convert bottles into lamps.
Drill a hole in the bottom of the bottle (carefully). Thread a cable through the hole and through the opening at the top of the bottle. Slide one of these over the cable and force it into the bottle opening. Connect the cable to the lamp holder. Screw the lamp holder onto the threaded section and voila another Mateus Rose bottle converted into a priceless lamp
Keith