overlock

An overlock, commonly called a serger in the United States, is a sewing machine or stitch that trims, sews, and finishes fabric edges in a single operation. It uses multiple threads and a built-in cutting knife to create an overcast edge that prevents fraying. The term overlock is widely used; serger is common in North America.

The machine operates with several threads, typically three, four, or five, and employs loopers and needles to form the stitch. A small knife trims the fabric edge as the threads interlock around it, producing a narrow, durable finish that allows some stretch when used on knits.

Common uses include finishing raw edges of garments, underwear, and stretchy fabrics; joining seams with a clean, unexposed edge; and finishing hems on apparel and linens. Overlock stitches are generally faster than conventional sewing and are valued for preventing unraveling without bulky seams, though they are not a substitute for all topstitching or reinforced seams.

Configurations vary by number of threads and intended fabric. Three-thread overlocks provide a light edge finish suitable for lightweight fabrics; four-thread models offer a stronger seam; five-thread variants combine seam construction with edge finishing for sturdy woven fabric seams. Domestic machines range from basic home models to high-volume industrial sergers.

Historically, overlock machines emerged in the late 19th and early 20th centuries as a means to speed seam finishing and edge protection. Today, sergers are standard in many garment facilities and increasingly common in home sewists’ workshops. Proper threading, tension adjustment, blade maintenance, and safety precautions are essential for reliable operation.