Go in with five by two strengthening strip (6)
I believe the answer is:
batten
'strengthening strip' is the definition.
(strip which fastens something)
'go in with five by two' is the wordplay.
'go in' becomes 'bat' (to be 'in' in cricket is to bat).
'with' means one lot of letters go next to another.
'five by two' becomes 'ten' (5 x 2 is 10).
'bat'+'ten'='BATTEN'
(Other definitions for batten that I've seen before include "Piece of securing wood" , "Wooden stiffening strip" , "Fastener for tarpaulin" , "Gain nourishment" , "Fasten securely - say the hatches" .)