The most common and most likely answer to this crossword clue is the 7 letter word THREADS
I've seen this crossword clue in The Guardian
T
H
R
E
A
D
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Buddy explains!
The straight part
We know that "Passes thin line through/series of linked posts" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case passes thin line through/series of linked posts = threads.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 THREADS mean?
THREADS noun- A long, thin and flexible form of material, generally with a round cross-section, used in sewing, weaving or in the construction of string.
- A continued theme or idea.
- A screw thread.
- A sequence of connections.
- The line midway between the banks of a stream.
- A unit of execution, lighter in weight than a process, usually sharing memory and other resources with other threads executing concurrently.
- A series of messages, generally grouped by subject, in which all messages except the first are replies to previous messages in the thread.
- A filament, as of a flower, or of any fibrous substance, as of bark.
- Composition; quality; fineness.
- To put thread through.
- To pass (through a narrow constriction or around a series of obstacles).
- To screw on, to fit the threads of a nut on a bolt
- Clothes.