Definition
A serger, called an overlocker in British English, is a machine that trims fabric edges and wraps them in thread loops, sewing and finishing seams in one pass.
A serger uses three to five threads fed through needles and two loopers, plus a pair of knives that cut the edge right in front of the stitch. The result is the overlock stitch found inside almost all ready-to-wear clothing.
What each setup is for:
| Threads | Use |
|---|---|
| 3-thread | Finishing edges, light seams, rolled hems |
| 4-thread | Sewing and finishing knit seams in one step |
| 5-thread | A chain stitch plus an overlock, for sturdy woven seams |
On knits, a 4-thread serger is fast and stretchy, and its differential feed keeps jersey from going wavy or gathers fabric on purpose. On wovens, it gives a quick, durable edge finish.
A serger does not replace a sewing machine: it cannot topstitch, insert a zip, sew a buttonhole or stitch away from the edge. It is a second machine, not a first one, and many sewists make years of clothes without one using a zigzag stitch and other finishes (see finishing seams without a serger).
In British English, the machine and its stitch share a name: an overlocker sews overlock. The double-row hem on T-shirts comes from a different machine, the coverstitch.