What serging does and why it matters
A serger (also called an overlock machine) trims fabric edges and seals them with thread in one motion, which a regular sewing machine cannot do. Instead of one needle and one bobbin, a serger uses two to five threads at once—typically two or three needles and one or two loopers underneath. The looper threads wrap around the edge of the fabric, creating a finished seam that won't fray and looks professional on both sides.
You don't need a serger to sew, but it saves time on seams that will show wear—like the inside of knit garments, activewear, or anything that gets washed often. A serger also lets you finish raw edges on woven fabrics so they don't unravel. Most sergers can also create decorative rolled hems and flatlock seams, which are stitches that lie flat and are often used on athletic wear.
Key Takeaways
- Threading a serger follows a specific path for each thread (usually marked with colored guides on the machine), and every thread must be seated fully in its tension dial before you sew.
- Serger tension has four separate controls—one for each needle and looper—and you adjust them one at a time by sewing a test seam on scrap fabric and watching how the threads interlock at the edge.
- The most common serger stitch is the 3-thread overlock, which uses the right needle, left looper, and lower looper to seal a fabric edge in one pass.
- Sergers cut fabric as they sew, so you do not need to trim seams afterward, but you must keep fabric edges aligned with the cutting blade guide to avoid cutting too much or too little.
- If thread breaks or loops appear, the problem is almost always incomplete threading or incorrect tension rather than a broken needle.
Threading the serger step by step
Before you thread, raise the presser foot—this opens the tension discs so thread can pass through them. Raise the needle bar to its highest point as well. Most sergers have colored thread guides (often printed on the machine or shown in the manual) that show the path for each thread. Start with the upper looper, which is usually the easiest to see.
Follow the colored path for the upper looper from the spool pin, through any guides above the machine, and into the upper looper eye. The thread should sit in the tension dial (the slot between two metal discs) before it enters the looper. Repeat this for the lower looper, then thread each needle from left to right. The right needle is usually the main cutting needle; the left needle is optional and used for certain stitches. Always thread needles from front to back, and make sure the thread clicks into the tension dial before it reaches the needle.
Once all threads are in place, hold the thread tails and turn the handwheel toward you two or three times to seat everything. If a thread does not move smoothly or feels stuck, stop and rethread that one—a thread that is not fully seated in a tension dial will break the moment you start sewing. Check your manual for the exact path, because thread routing varies by machine model.
Understanding and adjusting serger tension
Serger tension is not one dial—it is four separate controls, one for each thread. The goal is to make the threads interlock at the very edge of the fabric so no raw edge shows and no thread hangs loose. If the tension is wrong, you will see loops, puckering, or thread showing on one side of the seam.
Start by sewing a test seam on a folded scrap of the fabric you plan to use. Sew for 2 to 3 inches, then remove the fabric and look at the edge. The upper looper thread should wrap around the edge and meet the lower looper thread underneath—you should not see either one pulling or sagging. If the upper looper is too tight, it will pull the edge and pucker the seam; if it is too loose, it will hang off the edge. Adjust the upper looper tension dial by one number at a time, sew another test seam, and check again.
Once the upper looper looks right, check the lower looper the same way. Then check the needle tension (or tensions, if you are using two needles). The needle threads should sit inside the seam, not show on the back. This process takes patience, but you only have to do it once per thread type and fabric weight. Write down the settings in your manual or a notebook so you can return to them later.
The 3-thread overlock stitch and how to use it
The 3-thread overlock is the most common serger stitch and the one you will use for most seams. It uses the right needle, the upper looper, and the lower looper. To set it up, thread all three, then disengage the left needle (usually by removing it or flipping a switch—check your manual). Adjust tension as described above, and you are ready to sew.
Place your fabric under the presser foot with the edge you want to finish aligned with the cutting blade guide (a thin metal line or groove on the foot). The serger will trim a small amount of fabric as it sews—usually about 1/8 inch—so position the edge so that trim does not remove anything you need. Sew at a steady pace; sergers run faster than regular machines, but you do not need to rush. The machine will feed fabric automatically.
When you reach the end of a seam, sew 2 to 3 inches past the edge of the fabric to create thread tails, then stop. Raise the presser foot and pull the fabric away. You can tie off the thread tails or use a serger thread cutter (a small tool that comes with most machines) to find them. Some sewers straightforward leave the tails and trim them later.
Rolled hems and decorative finishes
A rolled hem is a narrow, finished edge that curves slightly and is often used on scarves, napkins, or the edges of knit garments. To create one, you usually switch to a 2-thread stitch (using one needle and the lower looper) and adjust the stitch length to a shorter setting. The machine will fold the fabric edge under as it sews, creating a tiny tube of thread around the edge.
Rolled hems require their own tension settings, so test on scrap fabric first. The edge should roll smoothly without puckering or showing raw fabric. If the fabric is very stretchy or slippery, you may need to use a stabilizer (a thin, temporary backing) to keep the edge from wavering.
Decorative stitches like flatlock use two needles and create a seam that lies completely flat, often with thread showing on one side for visual effect. These stitches are common on athletic wear and children's clothing. Refer to your manual for the specific thread and tension settings, as they differ from standard overlock.
Troubleshooting common serger problems
If thread breaks while you are sewing, stop when ready and rethread that thread completely. A broken thread usually means it was not seated in the tension dial or it caught on something during threading. Do not assume the needle is broken—serger needles rarely break, and rethreading fixes the problem 90 percent of the time.
If you see loops of thread on the back of the seam, the upper looper tension is too loose. If the seam puckers, the upper looper tension is too tight. If the needle thread shows on the back, the needle tension is too loose. Make small adjustments (one number on the dial at a time) and test again on scrap fabric.
If the serger is not cutting fabric, check that the cutting blade is not dull or bent. Most machines have a replaceable blade that you can swap out—refer to your manual for the location and replacement steps. If the blade looks fine, make sure you are feeding fabric straight into the blade guide and not pulling it sideways.
If the fabric is bunching or not feeding smoothly, lower the presser foot pressure slightly (many sergers have a dial for this). Lightweight fabrics and knits often need less pressure than heavy wovens. You can also try using a walking foot or stabilizer if the fabric is particularly slippery.
Serger maintenance and needle care
Serger needles are the same size and type as regular sewing machine needles, but they wear out faster because the serger runs at high speed. Replace the needle every 8 to 10 hours of sewing, or sooner if you notice skipped stitches or thread breaking. Always use the correct needle size and type for your fabric—a ballpoint needle for knits, a universal needle for woven fabrics, and a topstitching needle if you want a heavier thread line.
Clean the serger every few weeks by brushing lint and thread scraps out of the looper area with a small brush (usually included with the machine). Never use compressed air, which can blow lint deeper into the mechanism. Oil the machine according to your manual—some sergers need oil, others do not. If you do oil, use only the oil recommended by the manufacturer.
Store the serger with the presser foot raised and the needles in their highest position. This relieves tension on the springs and keeps the machine in good working order between projects.
Frequently Asked Questions
Can I use regular sewing thread on a serger?
Yes, but serger-specific thread is thinner and stronger, so it works better. Regular thread can break or create uneven stitches because sergers run faster and use more thread than regular machines. If you use regular thread, buy the best quality you can find and test on scrap fabric first.
Do I have to serge every seam?
No. Serging is most useful for seams that will show wear or for fabrics that fray easily. You can sew a regular seam on a sewing machine and then serge the raw edges afterward, or skip serging altogether if the garment will not be washed often or if the seams are hidden inside a lining.
What is the difference between a serger and an overlock machine?
They are the same thing. "Serger" and "overlock" are two names for the same machine. Some people use "serger" more often in North America and "overlock" in other regions, but they refer to identical machines.
Can I serge a seam that is already sewn on a regular machine?
Yes. Sew the seam first on a regular machine, then trim the raw edges and serge over them. This is called a "serged seam finish" and is common in garment construction. The serger will trim a small amount of fabric, so make sure your original seam allowance is wide enough to accommodate the trim.
Why does my serger keep skipping stitches?
Skipped stitches usually mean the needle is bent or dull, or the needle is not inserted correctly. Replace the needle first, making sure it is fully seated in the needle clamp. If skipping continues, rethread the needle thread completely. If the problem persists, the needle may be the wrong size or type for your fabric.