Just wanna know...
I've never done steeking but from my understanding it's basically a knitted area intended to be cut to make arm/neck holes. You sew around the area and then cut out the yarn.
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Steeks are areas of plain knitting which are knit into areas that are to be cut later for armholes, neck openings, or even down the front of the piece for cardigans.
They are used when working in the round, and are primarily used when knitting color stranded pieces (fair isle) or textured knitting (Ganseys) which would be more complicated to knit back and forth, as opposed to knitting in the round.
Hope this helps.
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