Bobbin winders, whether integrated into the machine or a portable machine, assist in winding the thread on the bobbin and uniformly dispersing the bobbin thread so that it is compatible with the top sewing machine thread tension. The bobbin is a temporary or permanent storage device for yarn or thread used in spinning, weaving, knitting, stitching, or lacemaking. Sometimes your bobbin could be winded by hand. If you have a few and the thread is thick it isnt so bad. But when you have many and thin thread then it could be very time consuming and tedious and thats where bobbin winders come in hany.