The sole of the foot has a slight indentation both in front and in back of the needle, allowing the free passage of the thread while reverse motion stitches are formed

This promotes balanced stitch formation where the fabric is moving back-and-forth while reverse motion stitches are formed

Owners of 9mm rotary models 1630 and 180 should consider using Foot #1C (9mm), which will better match the wider feed dog on these models