Metal Bobbins 45785 - Singer Featherweight
Singer Bobbin. Fits Singer 221, 222, 301, Kenmore 49, New Home ROTARY.
Outside diameter: 21.9mm - Height: 7.4mm - Axis diameter 6mm, 8 holes around rim.

Improperly loaded bobbins or bobbins that have the thread ‘tail’ caught around the outside of the bobbin or exposed can cause tension issues.
thread from the inside of the bobbin through a hole, then hold the thread tail close to the bobbin while winding so that it breaks off cleanly.
Old bobbins can have rust on them that will affect how they move within the bobbin case. Clean them with kerosene and emery paper if necessary.
Never use a bobbin that has been dropped on a hard surface or stepped on.