Square needles do two things that help create more consistent stitches. First, the flat surface encourages better hand posture in a way that leads to more consistent hand posture. More consistent posture gives more consistent stitches. Second, although stitches move easily up and down the flat surfaces, stitches past the tip of the needle move less freely around the needle so they don’t get pulled tighter or looser when the next stitch is worked. Not having the worked stitch tighten or loosen the neighboring stitches as drastically as can be done with round needles also improves how even and consistent the stitches appear, particularly when purling.
How do they encourage good posture?
Your fingers will rest on the larger flat surfaces instead of curling slightly around a round surface or pinching a smaller surface area. That slight curl or pinch can cause discomfort over years of frequent knitting or exacerbate existing problems. Additionally, stitches don’t twist around the needles easily, so you will consistently pick up your knitting in the same position as before when you take breaks.
