The most common and most likely answer to this crossword clue is the 7 letter word LORINER
I've seen this crossword clue in The Times
L
O
R
I
N
E
R
Buddy explains!

The straight part
We know that "Old metalworker" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case old metalworker = loriner.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does LORINER mean?
LORINER noun- A person who makes the bits and other metal parts of a horse's bridle, and other small metal pieces.