Feeling good, fastener finally accessing joint, lock securing device (4,4)
I believe the answer is:
hair grip
'lock securing device' is the definition.
I can't judge whether this defines the answer.
'feeling good fastener finally accessing joint' is the wordplay.
'feeling' becomes 'air' (I am not sure about this - if you are sure you should believe this answer much more).
'good' becomes 'g' (abbreviation).
'finally' indicates one should take the final letters.
'accessing' is an insertion indicator (inserted letters gain access).
'joint' becomes 'hip' (part of body).
The final letter of 'fastener' is 'r'.
'air'+'g'+'r'='airgr'
'airgr' placed within 'hip' is 'HAIR GRIP'.
Can you help me to learn more?
(Other definitions for hair grip that I've seen before include "It secures tresses" , "Something keeping coiffure in place" , "restraint with locks?" , "Aid to keeping coiffure in place" .)