Duke not prepared to stop building tower (7)

I believe the answer is:

drawbar

'tower' is the definition.
(bar which helps to tow a vehicle)

'duke not prepared to stop' is the wordplay.
'duke' becomes 'd'.
'not prepared' becomes 'raw' (I've seen this before).
'to stop' becomes 'bar' (I've seen this before).
'd'+'raw'+'bar'='DRAWBAR'

'building' is the link.

I've seen this clue in The Times.

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