A pinhead embedded in an old piece of wire (6)
I believe the answer is:
staple
'piece of wire' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps you can see a link between them that I don't see?
'a pinhead embedded in an old' is the wordplay.
'a pinhead' becomes 'p' (head letter of 'pin').
'embedded in' is an insertion indicator (I've seen this in other clues).
'an old' becomes 'stale' (I've seen this before).
'p' placed inside 'stale' is 'STAPLE'.
Can you help me to learn more?
(Other definitions for staple that I've seen before include "essential" , "Principle - fixer" , "Paper fastener - basic foodstuff" , "Main - way to fasten paper" , "e.g. rice, sweetcorn ..." .)