Jack may get this to fold up (5)
I believe the answer is:
knife
This clue could be a double definition.
'jack may' is the first definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'this to fold up' is the second definition.
The definition suggests a singular noun which matches the answer.
'get' is the link.
Can you help me to learn more?
(Other definitions for knife that I've seen before include "Piece of cutlery" , "Attack" , "Cutting implement - stab" , "Cutting instrument" , "Cutting utensil" .)