Overlockers make several stitches depending on how many threads you engage and which needles you use.
Four thread — two needles, two loopers. Sews a seam and finishes it in one pass, with a line of safety stitching. This is the standard for constructing knit garments.
Three thread — one needle, two loopers. Finishes an edge without constructing a seam. Use it to neaten seam allowances on wovens, or for a decorative edge. Which needle you use — left or right — changes the stitch width.
Two thread — one needle, one looper. A lighter finish for fine fabric, where a three-thread stitch would be too heavy and pull. Not all machines offer it.
Rolled hem — a narrow three-thread stitch with the stitch finger disengaged, so the edge rolls under. For scarf edges, chiffon hems and napkins.
Flatlock — loosened tensions so the seam pulls flat rather than standing up, giving a decorative ladder or loop effect. Used on activewear where a bulky seam would rub.
In practice most people use four thread for construction and three thread for edge finishing, and learn the rolled hem when they need it. The others are worth knowing exist rather than mastering immediately.
Questions people actually ask
Which do I use most?
Four thread, by a long way, if you sew knit garments. Three thread if you mostly sew wovens and want neat seam allowances.
Can an overlocker replace my sewing machine?
No. It cannot topstitch, sew a zip, make a buttonhole or sew a seam without trimming the edge. It is a second machine, always.
Last reviewed 2026-08-11