They make fast canal transport possible (5)

I believe the answer is:

locks

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'they' is the definition.
Both the answer and definition are plural nouns.
Perhaps you can see an association between them that I don't see?

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for locks that I've seen before include "Tresses" , "Clusters of hair" , "Securely fixes" , "Canal features" , "Door fasteners" .)

I've seen this clue in The Globe and Mail.

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