Turn to small personnel (5)
I believe the answer is:
screw
'turn' is the definition.
(I have seen 'fast turn' mean 'screw' so perhaps 'turn' could also mean 'screw')
'small personnel' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'personnel' becomes 'crew'.
's'+'crew'='SCREW'
'to' acts as a link.
(Other definitions for screw that I've seen before include "13ed fastener" , "Wage - prison officer" , "Fasten; propeller" , "Apply backspin (snooker)" , "Pay" .)