Pin I have put in to join sides of raft (5)
I believe the answer is:
rivet
'join sides of raft' is the definition.
'rivet' can be an answer for 'join'. I'm unsure of the 'sides of raft' bit.
'pin i have put in' is the wordplay.
'pin' becomes 'rt' (I can't justify this - if you can you should give a lot more credence to this answer).
'i have' becomes 'I've' (contraction of 'I have').
'put in' means one lot of letters goes inside another.
'rt' enclosing 'ive' is 'RIVET'.
'to' is the link.
Can you help me to learn more?
(Other definitions for rivet that I've seen before include "Clinch - bolt" , "join securely" , "Engross attention" , "Fasten with metal pins - enthral" , "Heavy fastening pin with head and hammered end" .)