The most common and most likely answer to this crossword clue is the 6 letter word STRAND
I've seen this crossword clue in The Guardian
S
T
R
A
N
D
More clues leading to the result STRAND
Buddy explains!

The straight part
We know that "thread" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case thread = strand.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 STRAND mean?
STRAND noun- The shore or beach of the sea or ocean; shore; beach.
- The shore or beach of a lake or river.
- A small brook or rivulet.
- A passage for water; gutter.
- A street (perhaps from the similarity of shape).
- To run aground; to beach.
- To leave (someone) in a difficult situation; to abandon or desert.
- To cause the third out of an inning to be made, leaving a runner on base.
- Each of the strings which, twisted together, make up a yarn, rope or cord.
- A string.
- An individual length of any fine, string-like substance.
- A group of wires, usually twisted or braided.
- A series of programmes on a particular theme or linked subject.
- An element in a composite whole; a sequence of linked events or facts; a logical thread.
- A nucleotide chain.
- To break a strand of (a rope).
- To form by uniting strands.