Second mate's checking empty icebreaker screws (7)

'screws' is the definition.
(both can mean to twist)

'second mate's checking empty icebreaker' is the wordplay.
'second' becomes 's' (common abbreviation).
'mate's' becomes 'pals' (both can mean a friend).
'checking' indicates putting letters inside (check can mean to control or arrest).
'empty' says to hollow out the word (remove centre letters).
'icebreaker' with its middle removed is 'ir'.
'pals' going around 'ir' is 'pirals'.
's'+'pirals'='SPIRALS'