The Bobbin Winder is supposed to wind the thread onto the bobbin smooth and even - with the thread flowing side-to-side as it winds. If your Bobbin is not winding evenly, it very well could be the position of the Tension Assembly Unit. Unscrew the screw that holds the Bracket in place and adjust it slightly to the left or right for even flow of thread to the Bobbin.
This is a Vintage Original part for those who are restoring a Singer Featherweight 221 or if your bobbin winder tension bracket is missing or somehow broken.
Screw not included but can be purchased separately.