A three-step zigzag makes three short stitches on each diagonal instead of one long one. The result is a stitch that spans the same width but lies flat instead of drawing the fabric together.
Why that matters. A single wide zigzag pulls inwards as it forms, which is what makes fabric tunnel along an edge. Breaking each swing into three shorter stitches spreads the pull, so the fabric stays flat.
What it is for.
Attaching elastic. The stitch stretches with the elastic and does not chew it. This is the standard stitch for elastic on lingerie and swimwear.
Finishing raw edges on lightweight fabric, where an ordinary zigzag would tunnel the edge.
Mending and darning tears, worked back and forth over a patch.
Joining fabric edge to edge on stabilised knits and on interlining, giving a flat join with no overlap.
Settings. Width 4 to 6 mm, length 1 to 1.5 mm as a starting point. Wider is generally better here, because the whole benefit is spreading the pull across a broader span.
On the dial it appears as a zigzag drawn with stepped rather than straight diagonals. Some manuals call it a serpentine stitch, a multi-step zigzag, or a tricot stitch.
One warning. It uses a good deal of thread and it is slow, so it is not a substitute for an ordinary zigzag on long straightforward seams.
Questions people actually ask
Is it stronger than a plain zigzag?
Not stronger, but flatter and more elastic. On elastic and on light fabric that behaviour matters more than raw strength.
Can I use it to finish seam allowances?
Yes, and it is a good choice on fabric that tunnels. On stable medium-weight cotton an ordinary zigzag is quicker.
Last reviewed 2026-08-11