It turns plug when new drive head is inserted (7)
I believe the answer is:
spindle
'it turns' is the definition.
(something which turns around)
'plug when new drive head is inserted' is the wordplay.
'plug when' becomes 'spile' (spile is a kind of plug. I am not sure about the 'when' bit.).
'head' indicates taking the first letters.
'is inserted' is an insertion indicator.
The first letters of 'new drive' is 'nd'.
'spile' placed around 'nd' is 'SPINDLE'.
(Other definitions for spindle that I've seen before include "Rod on which something revolves" , "This could be with knobs on" , "Slender rod on which thread is wound" , "Rod used in spinning" , "Rod serving as an axis of rotation" .)