DESC: The MyLock 634D with electronic control is the most advanced MyLock serger. It has 2 needles and 2, 3 or 4 thread overlock stitching. The differential feed ratio, which is adjustable from .05 to 2.25, provides increased control for handling all types of fabrics and for creating desired special effects. Threading is a breeze due to color-coded thread guides and a self-threading lower looper. Simply lay the thread into the guide, flip a switch, and the lower looper is threaded. The guide is automatically returned to its normal position when you turn the balance wheel. And when you lift the presser foot for rethreading, the thread tensions are automatically released so you can draw the thread smoothly.