The most common and most likely answer to this crossword clue is the 6 letter word WAISTS
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More clues leading to the result WAISTS
Buddy explains!

The straight part
We know that "they’re often belted" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case they’re often belted = waists.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 WAISTS mean?
WAISTS noun- The part of the body between the pelvis and the stomach.
- A part of a piece of clothing that covers the waist.
- The narrow connection between the thorax and abdomen in certain insects (e.g., bees, ants and wasps).
- The middle portion of the hull of a ship or the fuselage of an aircraft.
- That part of the upper deck of a ship between the quarterdeck and the forecastle.
- The middle part of anything.