The needle is the basic element of all knitting machines. The two main needle types are the “bearded” spring needle, invented about 1589, and the more common “latch needle”, invented in 1847.
The bearded needle, made from thin wire, has one end bent, forming an operating handle; the other end is drawn out and bent over, forming a long flexible tipped hook resembling a beard. A smooth groove, or eye, is cut in the stem or shank of the needle just behind the tip. In use this needle requires two other units, a sinker to form a loop and a presser to close the needle beard, allowing the loop to pass over the beard when a new stitch is formed. Bearded needles can be made from very fine wire and are used to produce fine fabrics.
The latch needle is composed of a curved hook, a latch, or tumbler that swings on a rivet just below the hook, and the stem, or butt. It is sometimes called the self-acting needle because no presser is needed; the hook is closed by the pressure of a completed loop on the latch as it rises on the shaft. Needles differ greatly in thickness, in gauge, and in length, and appropriate types must be selected for specific purposes. A 4-gauge needle, for example, is used for heavy sweaters, but an 80-gauge needle is required for fine hosiery. Source: https://www.britannica.com/topic/textile/