Silicone blue cap with spring release to push onto the internal baffle of coolers without the central spike system.
As the bottle is placed on the cooler the spring loaded valve rests on the central flat baffle and allows water to fill the cooler chamber.
Note these were common with older model coolers. New coolers have a lid with a spike to operate a throw away cap for bottle deliveries. Most coolers allow the top cover to be removed exposing the internal baffle for use with this part.