This is the mouth of my poor old Cornish fish (a knitting sheath that is strong enough to support long steel needles). It had worn until it was oval, and been re-enforced with different glues and epoxy. This morning it got a brass insert. We will see if that helps.
When I started learning about knitting sheaths, I was told that I would need curved gansey needles, which were no longer available. In fact the straight needles gansey needles work just best, but they aquire a curve as they are used over a period of hundreds of hours. Then, I pound them straight again and go back to my knitting. Curved needles were used with knitting sheaths for knitting miniatures, but that is an altogether different technique.
If you see a knitting sheath with brass insert (or a metal knitting sheath or knitting heart) then I know from sad past experience that it was used with metal needles. A knitting sheath with a metal mouth destroys wooden knitting needles.
One can knit socks without a knitting sheath. I could even knit hats, hoods, and scarves without my Goose Wing knitting sheath. I would knit slower, and there would be more stress on the hands and wrists, but I could do it. (Actually, I can make another knitting sheath in an hour with just my pocket knife and a candle.)
Real ganseys are another matter. Real. wind -proof ganseys (sailor's frocks) are another matter altogether. I cannot knit that tight, long enough to finish a gansey without a knitting sheath. Here I am testing the new "brass dentures" of my Cornish Fish, using 18" long US #1 double pointed steel gansey needles. The fish is tucked into my pants waist band over my right hip and the working needle is flexed forward under my right arm.
This is just back and forth swatching rather than real "in the round" knitting.
I am still amazed at how a knitting sheath tames these long needles. Such long needles are unmanageable without a knitting sheath. These gansey needles are even too long to use with a knitting pouch.
However, once you understand the technique, they make knitting a gansey ever so much easier and faster.
Another view showing how the yarn is held in my right hand. It is possible to knit "continental" style using a knitting sheath. Knitting continental style, one can knit even faster, but the fabric is significantly looser, and purling is more difficult.
Since my focus is on warm fabrics, I like to knit tightly, and I like stitches that add texture. Therefore, I usually hold the yarn in my right hand. Still, I knit fairly fast, and I can knit for exteded periods of time without much stress on my hands and wrists.