A coverstitch machine produces the flat, stretchy stitching commonly seen on T-shirt hems. Depending on the setup, one, two, or three parallel needle lines appear on top while a looper thread covers the raw edge underneath. The machine does not trim the fabric as it sews.
Coverstitch uses
Coverstitch is particularly useful for hemming jersey and knit fabrics because it remains flat and can stretch with the garment. It can also attach knit binding or become a decorative surface stitch. Many machines add a single-needle chainstitch, formed with one needle thread and a looper thread.
For an even hem, guide the folded edge so the looper thread catches it on the underside. Incorrect needle tension, looper tension, or presser-foot pressure may cause skipped stitches, tunnelling, or a wavy edge. The correct machine needle and a sample in the actual fabric help prevent these problems.
Coverstitch versus overlock
An overlocker or serger works along a raw edge, trims it with a knife, and wraps it in looper threads. A coverstitch machine can sew within the body of the fabric and leaves the edge uncut. A dedicated model is designed for coverstitch and chainstitch, not the standard three- or four-thread overlock seam.
Combination and “coverlock” machines
Some manufacturers offer combination machines that switch between overlock, coverstitch, and sometimes combined stitch formations. Conversion may involve disengaging the knife or upper looper, moving needles, changing the stitch plate or insert, and rethreading. The term coverlock is used inconsistently for a coverstitch machine or an overlock-coverstitch combination, so specifications are more reliable than the label alone.