Made from thick rubber, they seal well on nozzle diameters from about 1/4" to 3/4". Since only a part of the nozzle has to fall within this diameter range, it covers just about everything from toothpaste-type tubes up to quart glue-bottle tips.
These are a much better solution than putting a nail or screw in a nozzle tip. Also handy for capping the air inlet on air tools. Package of 20.