Nothing to secure a loose item in toolbox? (4)
I believe the answer is:
nail
'loose item in toolbox?' is the definition.
(nails might be found in a toolbox)
'nothing to secure a' is the wordplay.
'nothing' becomes 'nil' (eg nil is zero in football).
'to secure' means one lot of letters goes inside another (inserted letters are secured inside).
'nil' going around 'a' is 'NAIL'.
(Other definitions for nail that I've seen before include "Hit this on the head to be absolutely right" , "Fasten - detect and expose" , "Hammered individual" , "Part of finger" , "thing for keeping things together" .)