The most common and most likely answer to this crossword clue is the 8 letter word TWELFTHS
I've seen this crossword clue in The Daily Telegraph
T
W
E
L
F
T
H
S
More clues leading to the result TWELFTHS
Buddy explains!

The straight part
We know that "Parts" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case parts = twelfths.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 TWELFTHS mean?
TWELFTHS noun- One of twelve equal parts of a whole.
- An interval equal to an octave plus a fifth