Hard on the outside, hard on the inside nevertheless (6)
I believe the answer is:
though
'nevertheless' is the definition.
(I've seen this before)
'hard on the outside hard' is the wordplay.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'on the outside' means one lot of letters goes inside another.
'hard' becomes 'tough' (associated in meaning).
'h' put inside 'tough' is 'THOUGH'.
'on the inside' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for though that I've seen before include "Concessive conjuction" , "Despite the fact that" , "Even if" , "Nevertheless" , "However" .)