Kenmore 158.1802 Needle Centering Device

This device pushes the lower follower to the extreme right position. 

To use, put the dial on the CAM setting, push the follower release lever to the right, and insert the device with the upper follower in the hole.  The needle will now be in the center position.

The clearance is tight, so you may have to scale up or down in your slicer to get a perfect fit.