Difference between overlock & serger
There is very little difference between a serger and an overlock machine. In fact, sometimes an overlock is called a serger; the machines are used interchangeably. Both machines let you sew and overlock the edges of your garment's seams to achieve a clean, professional finish.
However, a serger has additional stitches besides the overlock, such as a flatlocking stitch, a chain stitch and a cover stitch. An overlock machine may have just the overlock stitch.
The flatlocking stitch can be used for sewing fabric pieces together or when you want your fabric pieces to lie flat. The chain stitch is created with one looper and one needle and looks much like a sewing machine stitch. The cover stitch creates two or three parallel lines on the top side of the fabric and loops on the underside of the fabric. All of these can be used as decorative stitches with decorative thread.
Three-Thread Overlock Stitch
The most common stitch for woven and lightweight fabrics is the three-thread overlock stitch. The three-thread overlock combines one needle, an upper-looper and a lower-looper to give the seams of your projects a nice finished edge. You can also use this stitch to put a decorative edge on a set of linen napkins or a tablecloth. The three-thread overlock is great for creating a rolled hem. A rolled hem adds that extra special touch to home decor projects like sheer curtains or the perfect trim to the dress you are making.
Four-Thread Overlock Stitch
A popular stitch for its durability is the four-thread overlock. It is like the three-thread overlock stitch, but it has two needles instead of one combined with an upper-looper and a lower-looper. It can be used in most of your projects ranging from clothing to crafts. It is best for piecing together knit fabric for T-shirts and children's active wear. You can use this stitch to create a make-up case or a new set of pillowcases for your bed.
Additional Overlock Stitches
The other overlock stitches are the two-thread and five-thread, although they are not used as much as the three-thread and four-thread overlock stitches. The two-thread overlock uses one needle and one looper thread, which creates a delicate stitch on lightweight fabrics like chiffon, organza or georgette. The five-thread overlock stitch is formed with two needles and three loopers. It can be used on loosely woven fabrics or clothes with stress-prone seams.