The piping foot will have its limitations when using thicker piping including the heavy jumbo cord and this is when the adjustable zipper foot will be invaluable. A screw-on type foot, it can be adjusted to fit snugly against the cord when covering your own piping or when attaching commercial piping. (AN EXCELLENT ALTERNATIVE!) For Janome Top Loaders Category B.
Janome Adjustable Zipper Piping Foot Cat B -B00GTSP9XA