Double locks in attempt to secure new file (4)
'double locks in attempt' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'to secure new file' is the wordplay.
'to secure' indicates putting letters inside.
'new' becomes 'n'.
'file' becomes 'rig' (I can't justify this - if you can you should give a lot more credence to this answer).
'n' put within 'rig' is 'RING'.
(Other definitions for ring that I've seen before include "Sound a doorbell" , "13's story of a 17" , "Dial" , "Circle; telephone" , "Arena; jewellery item" .)
'file' is the definition.
'double locks in attempt to secure new' is the wordplay.
'double' becomes 'ringer' (I've seen this before**).
'locks in' indicates putting letters inside.
'attempt' becomes 'bid' (bid is a kind of attempt).
'to secure' means one lot of letters goes inside another.
'new' becomes 'n'.
'bid' going around 'n' is 'bind'.
'ringer' enclosing 'bind' is 'RING-BINDER'.
(Another definition for ring binder that I've seen is " Loose-leaf folder".)