They prevent any escape from bottle-necks (5)
I believe the answer is:
corks
'they' is the definition.
Both the definition and answer are plural nouns.
Maybe they are linked in a way I don't understand?
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for corks that I've seen before include "Bungs" , "Bottle stoppers" .)