In order to best judge the importance of your needles, it helps to understand their anatomy and functions. The shank of an embroidery needle is the thick, upper portion of the needle that is clamped into the machine. Needles for most commercial embroidery machines are round, while for semi-professional machines, one side will be flat. The round shank is more economical to manufacture, which can have a positive effect for commercial embroiderers, where bottom-line pricing is often a must.
Source: Alice Wolf