Seriously, what the hell were you thinking?
It’s… a lemon reamer. No, it’s a… a… um…
The idea was to provide a more tactile experience for the knitter in order to reduce the incidence of dropped stitches, because, you know, pulling the yarn through those little loops by dragging the tip of one needle against the shaft of the other is so hard. As you can guess from the graphic illustrations, the yarn is caught beneath the head as the stitch is completed.
(Stop thinking that.)
Oh, look, you can still buy a kit to make the needle case. It’s on this page.
(I said STOP!!!)
On a serious note, it was meant to enable the knitter to work by feel alone. I wonder how this type of needle would fare with a yarn like Kidsilk Haze and similarly fine yarns, which can be frustrating to knit if you’re not watching your stitches. The yarn is so fine, you can barely feel it.
However, there’s a practical difficulty: this tip might be fine for the needle drawing the loop, but having that tip on the needle holding the live stitches might mess up the gauge. The stitch about to be knit would be near the narrow portion of the neck; a loop is drawn through, and then the original stitch needs to be lifted over that protruding head. Perhaps that’s why we don’t see this type of needle in any vintage collections.