Single point needles and cable needles do not work with knitting sheaths.
At one point, I put a lot effort into thinking about ways it could be done. Then, I asked, "Why do it?" What are the advantages of SPN and cables?
Well the cable's advantages are that it folds up and is not "pokey" in the knitting bag. I kid you not, that is a really big advantage - for knitters that take their knitting to tea parties. I often sit by my kitchen window, drink my tea, and knit. Then, cables have no advantage for me. If I go out to a tea party, I take shorter needles that fit in my knitting bag without being pokey.
Pocket sock needle case that doubles as knitting sheath.
Invite me to tea, and I will bring my knitting!
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