What is the difference between an overlocker and a coverstitch machine?

In a nutshell, they do look similar, but are both very different machines intended to produce different stitches. Let me explain further...each is designed for a specific task in garment construction and finishing. A regular sewing machine can perform many types of stitches but does not have the specialist looper mechanism of a cover stitch or overlocker machine, which is essential for creating cover hem and serging the edge of fabric as an overlocker produces. Here is a breakdown of the key differences between and overlocker and coverstitch machine:

Overlocker

Function: An overlocker is primarily used for finishing seam edges, trimming excess fabric, and preventing fraying. It creates a clean, professional-looking edge on fabric.
Stitches: An overlocker typically uses multiple threads (usually between 3 to 5) to create overlock stitches. These stitches wrap around the edge of the fabric to securing the raw edges.
Features: Overlockers can trim and cut off the raw fabric edge as they sew, which is useful for getting a professional-looking seamed edge. They are excellent for sewing knit fabrics and stretchy materials, as the stitches can stretch with these awkward to sew fabrics.
Common Uses: Seaming, edging, hemming, soft gathering, adding ruffles, and adding elastic to garments. Often used by dressmakers whilst making shirts, trousers, jackets, activewear and other difficult to sew stretch garments.
Example Stitches: 3-thread overlock, 4-thread overlock, rolled hem, and flatlock stitch.

Coverstitch Machine

Function: A coverstitch machine is used for hemming, joining, topstitching, and decorative stitching. It does not cut the fabric but creates a professional-looking hem that can stretch.
Stitches: Coverstitch models typically use 2 to 3 needles and 1 looper to create a coverstitch. This stitch looks like a parallel double row of straight stitches on the top side and an interlocking zigzag-like stitch on the underside.
Features: A coverstitch is particularly useful for hemming knit garments. The coverstitch can stretch and recover with the fabric. 
Common Uses: Hemming sleeves, pants, and creating decorative topstitching on garments. It's often used for the final hemming in T-shirts, sweatshirts, undergarments, sportsware and other knitwear. Most sweatshirts, purchased from high street stores, are manufactured from start to finish using a coverstitch machine.
Example Stitches: Narrow coverstitch, wide coverstitch, using two needles and triple coverstitch using three needles.

Key Differences Between and Overlocker and Coverstitch

Purpose: Overlockers are mainly used for finishing seams and preventing fraying, whilst coverstitch machines are used for hemming and topstitching. Both are used in dressmaking.
Stitch Types: Overlockers create overlock stitches around the edge of fabric, while coverstitch machines create a coverstitch to join pieces of material together, usually stretch matarials.
Fabric Cutting: Overlockers have a built-in blade to trim fabric edges, coverstitch machines do not.
Thread Usage: Overlockers use 1, 2 or 3 needles and usually between 3-5 threads, coverstitch machines use 2-3 needles plus a single looper thread.
Weight and Size: Both are similar weight and size. The more advanced models are larger by 2-5 cm and have a stronger chassis, hence a little heavier 1-2Kg

Both types complement each other in a sewing room, providing the necessary tools, together with a regular sewing machine to achieve professional finishes on garments, especially when working with knit fabrics.

Cutting Edge Combination Models

Options are now available to own a combination model known as a coverlock machine. This versatile machine can perform both coverstitch and overlock stitch functions. A coverlock machine is particularly advantageous for those with limited space and who do not frequently use coverstitch or overlock stitches.