The anatomy of perfect serger tension

The anatomy of the perfect serger tension, from on


Today I want to introduce MammaNene (Irene) – a sewing blogger who writes great tutorials on all types of sewing issues on her blog,! Irene is one of’s three blog contributors – and you’re in for a treat with her post today about finding perfect serger tension.

Hi SewMcCool readers! Hi Deanna :)

Since this is my very first time writing here, I’d like to present myself:

I’m MammaNene (Irene), a 30-something mom from North of Italy (I live in a tiny hamlet between the mountains, 820 meters above the sea).

I have a passion for sewing, refashioning, drafting, my blog and… my serger <3.

Just because I know that sometimes a relationship with a serger can be frustrating (as any other relationship, in fact), I’d like to share with you some of my little tips and tricks about serger’s tensions troubleshooting, learnt along my sewing journey; you’ll get the most if you’ll take a look to my 10 best beginner’s tips too, one of my most visited and pinned posts!

And this carries us to today’s topics: How do you create perfect serger tension? And how can you tell if your tension is wrong?

A couple of things to say first:

What is serger tension?

Tension on a serger (like on a sewing machine) is what decides the amount of thread that goes into the seam, it’s related to thread’s speed: if you increase tension, less thread will flow into the seam, and vice versa.

It depends on many factors, like type of thread, type of seam, fabric thickness, just to name some of them.

Just to be practical, you’ll probably need to loosen your tensions with:

  • heavier thread
  • thicker fabric
  • longer stitch (this mainly affects looper’s tensions)
  • narrower stitch (this mainly affects looper’s tensions)

Wait! First things first: you’ll need a threaded serger (need some help? Check my tutorial!)

When you buy a serger, usually, you’ve got it perfectly threaded!

A lot of people start sewing without taking more than a quick look to all those threads and their routes… then something goes wrong and… panic!

No need to! Let’s roll up our sleeves, we’ve got some work to do :)

… well, in fact I’ve already done the hard work for you…

Just a side note: maybe your serger isn’t exactly like mine (I have a Necchi 181, for the record) but they’re all similar. If you’re stuck, please ask for help!

Let’s take a look to this first photo: you can see that, on my Serger, the color code is:

green (left needle)

yellow (right needle)

blue (upper looper)

violet (lower looper)

I’ve threaded my serger with spools of thread with the same colors, to give you an easy reference to check when you’re in trouble…

Say “Thanks Mamma” and Pin this, quickly!


When you’ll be serging with 4 spools of the same color (or nearly the same color), it will be harder to understand which tension wheel you have to turn, and in which direction… Having pinned and checking this reference tutorial will guide you to fix it without doubts and in a short time, leaving you a lot of time for creating, having a coffee, go out with friends, you decide!

Find the balance: the Perfect Seam!

The following one is the perfect 4-thread seam: you can see that looper’s threads are meeting exactly on fabric’s edge and there are no puckers on needle threads, that look like two rows of straight stitches on right side…

… and tiny loops on the wrong side:

But what if tensions are messed up?

As a rule of thumb, on most sergers you should start with all four knobs on 4, usually it’s a great starting point for a 4-thread stitching.

Then, you have to take a look to your seam: is that perfectly balanced as mine? Well, I can go home, you’re great :)
If it’s not perfect, and you’re a visual person like me, you should take a look to some variations and understand what causes them: this will help you to learn which knob you’ll need to touch later!

To analyze tensions troubleshooting in-depth, I’ve sewn some samples putting tensions knobs on 0 (zero) and 9 (nine), just to see what happens in both front and back of the seam. You won’t find yourself on those extreme situations, but this will help you to understand how tension works.

  • Maybe it’s obvious, but you need to tighten tension (higher number) if you see loops and to loosen it (go to a lower number) when you can barely see the thread , that pulls and distorts everything.
  • Always start with small shifts of knobs, until you won’t “have an eye”

Let’s have a look to how your seams look like on front and back sides when tensions are set to “0” (first two photos of each group, front and back) or to “9” (second set of two pics, front and back), on:

– Left Needle (green):

Too low tension:

The lower row of stitches (green left needle) is no more a straight line, pulled up from the looper’s (blue in front, violet in back) threads. To fix it, just turn your left needle (green) knob to a higher number.

Too high tension:

And here you can see the green thread too tight: on front it’s pulling out the violet looper, on back side you can’t barely see some green spot! Turn down your left needle knob and everything will go better!

Right Needle (Yellow):

Too low tension:

Look at those yellow loops on both sides… it’s obviously needing a tightening action on left needle knob, to get back to a straight yellow seam line !

Too high tension:

Now you see how this yellow thread is pulling out our violet thread (lower looper) on front while on back is disappearing?

Action needed: loosen right needle knob!

Upper Looper (Blue):

Too low tension:

Loopers should meet each other on fabric’s edge, midway. Here the lower looper is so loose that is looping on back side… better turn its knob to a higher number!

Too high tension:

And this is the opposite situation: a too tightened upper looper tension is pulling up green left needle thread, distorting it, while it’s pulling violet thread on front side

Lower Looper (Violet):

Too low tension:

Last one: the lower looper acts as the upper looper, just be sure to touch the right knob:

Remember that your Upper Looper (blue) sits on front (or up) side of the seam,

while Lower Looper (violet) is on the back (or low) side of the seam .

On the first couple of pics you can see a lower looper without enough tension:

Too high tension:

And here the same lower looper (violet thread) is too tight: you can’t see it on front of the seam and it pulls the upper looper (blue) and the left needle (green) on back of the seam, failing to meet the other looper’s thread on the edge of the fabric!

Obviously, in real life you’ll experience a combination of two or three thread’s tensions messed up.

When I have to fix more tensions, I like to follow this order:

  1. fix left needle‘s tension
  2. fix loopers tensions
  3. fix right needle‘s tension.

But, what if your tensions are messed up but you think tension disks are correctly set?

Here are some of the questions I usually ask myself:

  1. Do I have a thread caught under a cone or spool?
  2. Is the thread following a wrong way, skipping a thread guide?
  3. Are there any threads that wrap twice around a thread guide?
  4. Did I check my needle condition? Is it inserted in the right way, have I chosen the right one (right type and size, basing on fabric)?
  5. Did I check for tangled thread on the stitch fingers or feed dogs, or loopers?
  6. Is my thread guide pole in its higher position (the first thread guide right after the spools)?
  7. Did I check for lint or bird’s nests of thread between tension disks? Your serger loves a good air blow from a compressor or a simple canned air!
  8. Is thread perfectly seating on tension disks? Floss them, eventually, just to be sure!


And now… what about My Bonus Tip for you… here’s my animated infographic about

how-to unpick a 4-thread serger seam

Pin it now, you’ll thank me later 😉

I hope you enjoyed my little rant about serger’s tensions. Let me know if something was unclear!

And if you want to know more…please see my follow-up post so you can do MORE with your serger! Learn all about how to create different serger stitches….there’s even a great serger infographic!

I’ll be more than pleased to answer to your comments, if you’ll be so nice to leave me a couple of words about your relationship is with your serger… Or anything else!

See you here, if you like, next month :)
Hugs from Italy,

MammaNene @


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  1. Elisabetta says

    Hooray Irene, go go go
    You definitely made the best tutorial ever!
    I am so happy I met you and I’m so glad you made it, big steps to fame ^_^
    Love you

  2. Christine Ousley says

    Wow, what a great tutorial. I love all of the pictures. They will be so helpful to pinpoint the problem when serger tensions arise. Thanks so much for all this great info!

  3. Tricia says

    Thank you, thank you, thank you.
    I’ve been trawling the internet to help solve my problem with my tension (well my serger’s tension) and then I come across your brilliant site. You explain things so well and what a bonus to have pictures.
    So now I’m about to go and get rid of these annoying loops and get on and make something!
    Once again, many thanks and I’m sure I’ll be popping back again for some more advice!

    • Deanna McCool says

      So happy you like it! Irene (Mamma Nene) of will have another serger tutorial this upcoming week – and you can always check out her blog for more great tips!! :) Now…to solve *your* tension problems…you might have to go to a different type of blog, lol!

  4. Loralee says

    My serger wants to gather EVERYTHING I put through it, and if I try to smooth the gathers out the threads break (the left needle thread), and the piece loses its stretch. What could be causing this?


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