Be sure to unplug the machine before you replace the bobbin case in it. Otherwise, electric shock or injury may result.
Be sure that the bobbin case is correctly installed. Otherwise, the needle may break.
Never use a bobbin case that is scratched; otherwise, the upper thread may become tangled, the needle may break, or sewing performance may suffer.
For a new bobbin case (part code: XC3153-251 (green marking on the screw), XC8167-451 (no color on the screw)), contact your nearest authorized dealer or service center.
If the needle plate has been removed it is especially important to reinstall the needle plate and tighten the screws prior to installing the bobbin case.
Insert the bobbin case so that the projection on the bobbin case aligns with the spring.
Projection 
Spring
