Definition
An overlock is a stitch that wraps thread loops around a fabric edge while knives trim it, sewn by a serger to finish edges or sew stretchy seams.
Overlock is the stitch on the inside seams of almost every ready-made T-shirt. In British English, the machine that makes it is an overlocker; in American English, a serger. To overlock and to serge mean the same thing.
The stitch comes in several forms:
| Stitch | Threads | Use |
|---|---|---|
| 3-thread overlock | 1 needle, 2 loopers | Edge finishing and light seams |
| 4-thread overlock | 2 needles, 2 loopers | Construction seams on knits, with an extra row for strength |
| Rolled hem | 2 or 3 threads | Tiny wrapped edge on chiffon, ruffles and napkins |
| Flatlock | 2 or 3 threads | Flat decorative seam for sportswear |
An overlock stretches with the fabric thanks to its loops, so it is the standard seam for knits. On wovens, it is mostly used to finish raw edges, before or after the seam is sewn with a straight stitch.
Many sewing machines offer an "overlock" or overcast stitch that imitates the look by stitching over the edge, without trimming it. It works for finishing edges, best with an overcast foot, but is slower and less neat than a true overlock.
If knit seams come out wavy, adjust the serger's differential feed. For finishes on a regular machine, see zigzag stitch and seam finish.