Proverbially hard things to drive home (5)

I believe the answer is:

nails

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'proverbially hard things' is the definition.
The definition and answer can be both man-made objects as well as being plural nouns.
Maybe you can see an association between them that I don't see?

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for nails that I've seen before include "Claws" , "Cock's crest" , "Metal spikes" , "Fixing spikes" , "Fastens with spikes" .)

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

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