3/4 Thread with easy to thread lower looper and rolled hem switch. When you want to make the most of your serging time, with professional results, the MyLock 634 is unmatched. It has 2 needles and 2, 3 or 4 thread overlock stitching. Threading is a breeze due to color-coded thread guides and an easy lower looper threading system. The MyLock 634D also lets you quickly switch to rolled hemming without changing the needle plate.