Needles are an essential component of machine embroidery. They have a language of their own: eye, groove, point. Here is a primer for translating basic embroidery machine needle terminology.
The shank is the part of the needle that is inserted into the sewing machine. The shank is the heaviest part of the needle and is designed to minimize needle movement by attaching it firmly to the needle bar.
Needles range in size from very fine 60/8 to a heavy duty needle 120/19. Most needles use the two-number measuring system. The higher number relates to the metric system and defines the needle shaft diameter in hundredths of a millimeter. The lower number relates to the system in the U.S. and is an arbitrary number also used to indicate needle shaft diameter.
The groove protects the thread by hiding it as it passes through the fabric on its way to join with the bobbin thread. Some needles have exaggerated groves to protect the thread when sewing on particularly dense fabric. A needle that is too fine for the size of thread used will result in inconsistent stitches and broken thread.
The eye of the needle is the hole through which the thread passes. As the size of the eye increases, the size of the shaft increases to support it.
The point of the needle is a primary distinguishing feature in needles. Points can be sharp or ball, or a hybrid of both. The angle of the point can be slender or acute. The point can be centered or eccentric. All are designed for a specific purpose and all give the operator unique applications.
The scarf is the cut away portion on the back of the needle just above the eye. This area accommodates the hook mechanism as it rotates past the needle to engage the thread loop formed by the lifting needle. The shape and position of the scarf increases the consistency of stitching with various threads and fabrics.
Here are links to some of the major needle manufacturers. Each features a variety of free educational resources.