The Right Seam Guide in Shaft is used for Cover- and Chainstitch to create parallel seams to lines, existing seams or the fabric edge on the right side of the Presser Foot.
 
Seam Guide in Shaft Left can be used for Overlock, Combostitch, Coverstitch and Chainstitch. It is used to follow lines or existing seams on the left side of the Presser Foot. It's also used to guide strips of fabrics at an equal distance, for example for sewing ribbons.
The set contains both, the Right and Left Seam Guide.