Wheels shy tourist now and then (7)

I believe the answer is:

castors

'wheels' is the definition.
(castor is a kind of wheel)

'shy tourist now and then' is the wordplay.
'shy' becomes 'cast' (both can mean to throw).
'now and then' means one should take alternating letters (letters taken on a regular basis, now and then).
The alternate letters of 'tourist' are 'ors'.
'cast'+'ors'='CASTORS'

(Another definition for castors that I've seen is " Small wheels".)

I've seen this clue in The Guardian.

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