Knitting in garret - terrible pain (6,6)

I believe the answer is:

garter stitch

I'm a little stuck... Click here to teach me more about this clue!

'knitting' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps they are linked in a way I don't understand?

'garret terrible pain' is the wordplay.
'terrible' is an anagram indicator.
'pain' becomes 'stitch' (pain in the body).
'garret' is an anagram of 'garter'.
'garter'+'stitch'='GARTER-STITCH'

'in' is the link.

Can you help me to learn more?

(Another definition for garter stitch that I've seen is " Plain knitting method".)

I've seen this clue in The Daily Express.

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