Wears down one small nail with excess edges (7)

'wears down' is the definition.
'abrades' can be an answer for 'wears' (I've seen this in another clue). I am not certain of the 'down' bit.

'one small nail with excess edges' is the wordplay.
'one' becomes 'a' (a thing is one thing).
'small nail' becomes 'brad' (I've seen this in another clue).
'with' means one lot of letters go next to another.
'edges' means to remove the middle letters (I've seen 'edging' mean this (edging means the letters on the edges)).
'excess' with its middle removed is 'es'.
'a'+'brad'+'es'='ABRADES'

Can you help me to learn more?