What is a serger? A serger, also called an overlocker or an overlock machine, is a specialized sewing machine that uses an overcasting stitch to simultaneously sew a seam and seal the raw seam edges.
This makes it a powerful tool, one that allows you to create strong, professional-quality seams and edges.
At the same time, a serger is quite different from a regular sewing machine and there are some tasks it cannot do. An overlocker, therefore, should augment, rather than replace, your regular sewing machine.
How is a Serger Different from a Sewing Machine?
The first difference you’ll notice is appearance, but sergers also have features, such as loopers and differential feed mechanisms, that regular sewing machines do not have.
A overlocker accomplishes different functions from a standard sewing machine as well, and we’ll get to those shortly.
Anatomy of a Serger
You’ll know an overlock machine by its shape and size. Sergers are generally smaller than regular sewing machines and many also have a squarish shape to their outer casing.
- Thread tree
- Presser foot pressure adjustment screw
- Spool pin
- Spool support
- Thread take-up cover
- Upper knife
- Presser foot
- Material plate cover
- Spool stand (thread tree support)
- Left needle thread tension dial
- Right needle thread tension dial
- Presser foot lifting lever
- Hand wheel
- Upperlooper thread tension dial
- Lowerlooper thread tension dial
- Front cover
- Material side plate (for overlock stitch)
- Main power switch and light switch
- Stitch length adjustment dial
- Differential feed ratio adjustment lever
- Lowerlooper threading lever
- Stitch finger
- Stitch width lever
- Free-arm cover
- Bed extension
- Knife lever
Sergers have multiple thread spools for, you guessed it, multiple threads. You can find overlockers with two, three, four, five, or even more threads. Often, overlockers use cone thread, rather than thread on spools.
An overlock machine also uses multiple needles. Generally speaking, one needle sews a straight row, while the other interacts with the looper (or loopers) to wrap thread around the seam edges. These two actions happen simultaneously and a serger has no bobbin thread.
Regular sewing machines have one set of feed dogs, while overlockers have two. You can use a serger’s differential feed mechanism to adjust both sets of feed dogs, so that they move their portion of fabric at the same speed or at a different pace to one another. 
This can come in useful for:
- Preventing puckering while sewing lightweight fabrics
- Intentionally gathering your fabric while sewing
A serger also has a knife or blade (sometimes it has both!) for trimming seam edges while you sew.
Here’s a look at a simple Singer serger.
What are sergers used for?
As we’ve already touched upon above, an overlocker is used differently to a regular sewing machine.
You might use a regular sewing machine for:
- Decorative stitching
- Monogramming and embroidery
A serger cannot do any of these things. Instead, an overlocker does overcasting, and you can use this for various sorts of tasks, including:
- Overcast seams
- Rolled hems
- Sewing stretch fabrics and knits
- Creating pleats, gathers, and pintucks
- Making “lettuce” edges
Why Do Sergers Have Multiple Threads?
Sergers use anywhere between two and eight threads. The most common arrangement is three or four threads.
One thread sews a straight stitch, which creates the seam. The remaining threads zigzag and loop around the seam edges. This seals the edges and keeps them from fraying. It’s particularly useful when working with knit fabrics.
A regular sewing machine uses a top thread and a bobbin thread. A serger machine, on the other hand, uses one or more looper threads instead of a bobbin thread.
How many threads do you need?
That depends on the task you wish to accomplish. A three and four thread serger can accomplish most jobs. But there are times when you might want a two-thread overlocker, or one that uses more than four threads. 
Here are some common uses of different serger types:
- True safety stitch
- Decorative edging
- Finishing edges of light fabrics
- Mock flatlock stitch
- Blind hem
- Two-thread overlock
- Stretch fabrics
- Strong, wide serged seams
- Rolled hem
- Mock safety stitch
- Three thread overlock
- Simultaneous chain stitch while overcasting seams
- Simultaneous safety stitch while overcasting seams
- Four thread overlock
More than four threads
- Chain stitch
- Simultaneous strong seam and heavy-duty seam finish
In general, you should use no less than four threads to serge items that will be subject to heavy stress.
Why Do Sergers Have Knives?
Many overlockers have a knife that trims the seam edges while you sew. Some models have two blades, which work like scissors to accomplish this task.
Some overlock machines allow you to choose between using the knife or not, depending on your task. For example, with some kinds of decorative sewing, you may not want to use it.
Are serger knives safe?
A serger’s knife is absolutely safe, provided you follow the manufacturer’s safety instructions.
What Do Sergers Do Well?
People use sergers for two primary reasons: creating strong, sealed seams, and preventing fraying of fabric edges. Overlockers are also excellent if you’re working with knits and stretchy fabrics.
However, an overlocker is also good for different types of decorative edging and you can also use it to create rolled hems. An overlocker’s differential feed mechanism also makes it easy to do pintucks and gathers.
Check out our article on creating decorative edges for more special effects info.
What Can You Not Do With a Serger?
Although an overlocker is a powerful tool for certain jobs, there are other tasks for which you’ll still need your regular sewing machine. These include:
- Decorative embroidery stitches
- Straight stitching
In addition, there are certain projects, like quilts, where the reinforced seams created by a serger are too bulky, or otherwise undesirable. In these cases, a regular sewing machine is still the best choice.
Should Every Sewing Room Have a Serger?
An overlock machine, as you can see, is a specialized piece of equipment made to do a specific set of tasks.
Does every sewing room need one? Probably not. If your main craft is quilting or machine embroidery, then you probably won’t use a serger very often.
On the other hand, if you sew mainly clothing and housewares, an overlocker can make your life a lot easier, and your projects a lot more polished.
So, should every sewing room have a serger? It’s fair to say that owning an overlocker isn’t necessarily vital for everyone who enjoys sewing.
A more salient question is to ask whether your sewing room needs one. And only you can answer that!
What Is A Serger? Final Thoughts
A serger is a specialized sewing machine for making strong, sealed seams and decorative edges. It can make your garments and housewares more robust and give them a professional finish. And once you get the hang of using an overlock machine, it can be a lot of fun.
At the same time, a serger can’t do everything. It’s not a replacement for your regular sewing machine. Rather, it’s another tool for your crafting arsenal.
Do you enjoy using an overlocker? What are some things our readers should know about working with them? Please tell us in the comments below!
- Brother USA | 1034D Product Catalog | https://www.brother-usa.com/-/media/brother/product-catalog-media/documents/2020/02/21/18/00/884-345_om07_enes.pdf
- FPO | Differential Feed Mechanism for a Sewing Machine | https://www.freepatentsonline.com/3611817.html
- Insook Ahn | Selecting an Overlock Sewing Machine | https://aces.nmsu.edu/pubs/_c/C218/welcome.html