fine line; thin line
Refers to a very thin line, often drawn or engraved. Also used figuratively for a delicate boundary.
The craftsman carved a line as fine as a thread.
weight of thread; thread weight
Used in contexts like sewing or textile work to refer to the thickness or weight of thread.
For this fabric, it's better to use a slightly thicker thread.
slit-eyed; narrow-eyed
Colloquial and often vulgar term for eyes that are very narrow, like slits. Can be derogatory.
That guy has slit eyes, and you never know what he's thinking.