Pin to act on short spring (5)
I believe the answer is:
dowel
'pin' is the definition.
(peg for fixing together components of a structure)
'act on short spring' is the wordplay.
'act on' becomes 'do'.
'short' means to remove the last letter.
'spring' becomes 'well' (both can mean a source of water).
'well' with its final letter taken off is 'wel'.
'do'+'wel'='DOWEL'
'to' is the link.
(Other definitions for dowel that I've seen before include "Wooden peg" , "Lowed (anag.)" , "Short peg used as a fastener" , "Pole" , "Peg used for fastening two adjacent parts of a structure" .)