Understanding the basic needle parts helps to better understand the needle's functions.
The needle shank is the area inserted in the machine and held in place by a screw or clamp. Most household sewing machine needles have a flat shank side. This should be positioned opposite the threading path. On most of the newer machines the flat side goes to the back.
The groove is an indentation down the front of the needle shaft which leads the thread from the last machine thread guide to the needle eye.
The needle shaft is the long portion that penetrates the fabric with each stitch.
The eye is the receptacle for the thread and should allow it to pass through smoothly and freely for proper stitch formation.
The point is the sharp or rounded end penetrating the fabric.
The scarf is an indentation at the back of the needle above the eye. A long scarf helps eliminate skipped stitches by allowing the bobbin hook to pick up the upper thread more easily.