The most common and most likely answer to this crossword clue is the 10 letter word COMPONENTS
I've seen this crossword clue in The Daily Telegraph
C
O
M
P
O
N
E
N
T
S
Buddy explains!
The straight part
We know that "spare parts" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case spare parts = components.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 COMPONENTS mean?
COMPONENTS noun- A smaller, self-contained part of a larger entity. Often refers to a manufactured object that is part of a larger device.