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For a coverstitch machine, the most common setup is polyester sewing thread ticket 120 for the needles and textured polyester or polyamide for the looper. The needle threads form the parallel visible rows on top, while the soft textured thread in the looper covers the raw edge underneath and lets the seam stretch together with the jersey. The right combination solves most problems with breakage and wavy hems.
How thread works in a coverstitch machine
A coverstitch machine is different from an overlocker: it does not cut the edge but makes a chain stitch with two or three needles and one looper. On top you see two or three parallel rows of straight stitch, while underneath the looper thread zigzags between them and covers the raw edge. That is why the seam is both elastic and decorative – it is used for hems on T-shirts, sleeves, bodysuits, sports leggings and lingerie, and for attaching elastics and bindings.
Because this is a chain stitch, the thread works differently from the lockstitch seam of a straight-stitch machine. If the looper thread breaks or is pulled out, the seam can unravel along its entire length. That is why choosing a strong, even thread for the looper is more important than it seems.
Coverstitch machine thread: needles and looper
Needle threads
For the needles, use a smooth spun polyester or core-spun thread with ticket 120 (for very fine jersey, 150–180). The thread is visible on the right side, so it must be even, free of knots and an exact colour match. Textured thread in the needle is rarely used – only when you want a maximally stretchy seam, for example on swimwear, and the machine can handle it.
Looper thread
This is where the advantages of textured (bulked, "fluffy") thread are greatest:
- it spreads out and covers the edge densely without showing through;
- it stretches together with the fabric and does not break when the garment is put on;
- it is soft to the touch – important for lingerie, children's clothing and sportswear, where the seam rests against the skin;
- it is consumed faster than the needle threads, so it is bought on larger cones.
With woven fabrics, or when the seam does not need to stretch, ordinary spun polyester of the same thickness as the needles can also be used in the looper.
Choosing by fabric
| Fabric | Needles | Looper |
|---|---|---|
| Fine single jersey, viscose, lingerie | Spun polyester ticket 150–180 | Textured polyamide or polyester |
| Cotton jersey for T-shirts | Spun polyester ticket 120 | Textured polyester |
| Elastane, swimwear, leggings | Spun polyester 120, preferably textured | Textured polyamide |
| Sweatshirt fleece, brushed-back jersey | Core-spun or spun polyester 120–100 | Textured polyester |
| Knits (rib, interlock) | Spun polyester 120 | Textured or spun polyester |
How many cones are needed
A three-needle coverstitch machine works with four threads at the same time, a two-needle one with three. In a garment factory it is convenient for all needle threads to come from the same batch and colour, so there is no shade difference between the rows. The looper thread is consumed fastest, so when planning the order it is sensible to allow more cones for it. As for colours: the needle threads are matched exactly to the fabric, while the looper can be a close neutral tone if the inside is not visible.
Tension and settings
Most complaints about coverstitch seams are actually setting problems, not thread problems. Here are the main guidelines:
- Needle tension. Start from a medium value. If a "tunnel" – raised fabric – forms between the rows, reduce the needle tension or increase the differential feed.
- Looper tension. Textured thread requires lower tension than spun polyester. If there are overly loose loops underneath, increase it gradually.
- Differential feed. On stretchy jersey, a wavy hem is usually corrected with a feed above 1.
- Needles. Use stretch or ballpoint needles for jersey to avoid skipped stitches.
- Threading. Thread the looper first and the needles afterwards – this way the needle threads catch the looper thread correctly.
How to secure the end of the seam
A chain stitch unravels if you pull the looper thread from the end. So at the end of the hem, pull the needle threads through to the inside and tie them off, or overlap the seam at its start on circular hems. In production this step is controlled, especially on children's clothing.
Common mistakes
- A fine embroidery thread in the looper instead of a textured sewing thread – the seam breaks when the garment is put on.
- Different brands of thread in the needles – the rows differ in sheen and thickness.
- Too much looper tension with textured thread – the bulk and coverage are lost.
- Old, dried-out thread – the chain stitch breaks and unravels.
Testing before series production
Before putting a new thread-and-fabric combination into series production, sew a few hems on a sample and check them: stretch the seam fully widthwise, wash the sample at least once and see whether the looper thread covers the edge evenly. Also compare the colour of the needle threads with the fabric in daylight. Record the tension and differential feed settings so you can reproduce them in the next order with the same fabric.
If you attach elastic with a coverstitch machine, choose a suitable elastic according to the width of the attachment. You will find more about the other types of thread in the threads category.
Coverstitch threads from Polkom
Polkom supplies sewing threads wholesale to knitwear factories and clothing brands – polyester for the needles and textured for the looper, in a wide range of colours. As a manufacturer and supplier of garment accessories, we can match the colour to a fabric sample and send a sample for testing on your machines. Write to us via our Contact page with the type of jersey, the number of needles and the colours required to receive a quote.
