If your Featherweight Bobbin Winder seems loose and floppy then it might just need to have the cupped washer turned around. (The cupped side faces away from the head of the screw.) However, if your washer is missing, then this is a replacement to be applied to the Bobbin Winder screw.
If you have issues with Bobbin Winding - take a good look at the condition of the Bobbin Winder Wheel - if it is old, grey or brittle, then it is time to replace, making bobbin winding easier and more efficient.
Bobbin Winder #45929 Singer 221 - 222 Featherweight