The most common and most likely answer to this crossword clue is the 5 plus 3 letter word ALLEN KEY
I've seen this crossword clue in The Guardian
A
L
L
E
N
K
E
Y
Buddy explains!
The straight part
We know that "Turn your hand to flat-pack furniture with this?/Turn your hand to flat-pack furniture with this?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case turn your hand to flat-pack furniture with this?/turn your hand to flat-pack furniture with this? = allen key.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.