Overlock and coverstitch machines get confused constantly, and it is easy to see why: both run off cones of thread, both are fast, both show up on the same t-shirt. But they do opposite jobs, and once you see the actual stitch each one makes, you will never mix them up again.
The short version: an overlock works on the edge of the fabric. A coverstitch works on the surface of the fabric. Neither replaces the other.
The one thing both machines have in common: no bobbin
This is the fact that explains everything else, and it is usually left out.
A lockstitch machine (stitch class 301) forms its stitch by locking a needle thread against a bobbin thread. Overlock and coverstitch machines have no bobbin at all — they use loopers, and every thread comes from a cone on the stand.
That single difference is why:
- They run at 5,500–6,500 stitches per minute in production. No bobbin means no stopping to change one.
- They consume far more thread per metre of seam than a lockstitch. Budget for it.
- Their seams are elastic — chain-type stitches stretch with knit fabric instead of snapping.
- Their seams unravel if you pull the chain from the wrong end, unlike a lockstitch that locks on itself. Ends have to be secured.
Overlock (serger): finishes and seams the edge
An overlock machine trims the raw edge with a knife and wraps thread around it in the same pass. On knits it can seam and finish simultaneously; on wovens it is usually finishing an edge whose seam was made elsewhere.
The knife can be disengaged when you do not want to trim.
The stitch classes (ISO 4915, class 500)
| Class | Configuration | Typical use |
|---|---|---|
| 503 | 1 needle, 2 threads | Light edge finishing, blindhemming, carpet overedging |
| 504 | 1 needle, 3 threads | The classic overlock. Finishing and light knit seaming |
| 514 | 2 needles, 4 threads (“mock safety”) | The production workhorse for knitwear seams |
| 516 | 5 threads — a 401 chainstitch plus a 504 overedge, formed together | True safety stitch. Seams and overedges wovens in one pass — jeans, workwear, trousers |
Machines run from 2 up to 6 threads depending on configuration. If someone tells you an overlock is “3 to 5 threads,” they have not seen the ends of the range.
Shop overlock and safety stitch machines.
Coverstitch: hems and topstitches the surface
A coverstitch machine lays two or three parallel needle rows on the face of the fabric with a looper thread covering the underside. It does not cut. It is what makes the hem of a t-shirt, the cuff of a sweatshirt, the waistband of leggings and the neckline binding on activewear.
Because the seam is a chain-type stitch, it stretches with the garment — which is exactly why a lockstitch hem on a knit t-shirt pops the moment someone pulls it over their head.
The stitch classes (ISO 4915, classes 400/600)
| Class | Configuration | Result |
|---|---|---|
| 406 | 2 needles, 3 threads | Bottom coverstitch |
| 407 | 3 needles, 4 threads | Bottom coverstitch, wider |
| 602 | 2 needles, 4 threads | Top and bottom cover |
| 605 | 3 needles, 5 threads | Top and bottom cover, widest |
The practical trade-off: because a coverstitch does not trim, your panels have to be cut accurately before they reach the machine. There is no knife to clean up a wandering edge.
Shop coverstitch machines.
Side by side
| Overlock | Coverstitch | |
|---|---|---|
| Works on | The edge | The surface |
| Stitch classes | 503 / 504 / 514 / 516 | 406 / 407 / 602 / 605 |
| Trims fabric | Yes (knife can be disengaged) | No |
| Bobbin | None — loopers | None — loopers |
| Threads | 2 to 6 | 3 to 5 |
| Main job | Seam and/or finish the edge | Hem, topstitch, bind, flatseam |
| Can it replace the other? | No. They are sequential operations, not alternatives. | |
Differential feed: the adjustment that decides your seam quality
Both machine types have two independent sets of feed dogs, front and rear, and you can set the ratio between them — typically from around 0.7 to 2.
- Ratio above 1 — the front feeds faster than the rear, gathering the fabric. Prevents the wavy, stretched-out edge you get on jersey and rib.
- Ratio below 1 — stretches the fabric slightly as it feeds. Used for lettuce edges and for keeping woven edges flat.
If your knit hems come out rippled, the problem is almost never the machine. It is the differential feed setting.
Flatbed or cylinder arm? (coverstitch buyers, read this)
This is the decision people regret most, because both look similar in a photo.
- Flatbed — for hems you can lay open, neckline binding, and flat seaming. The SPEEDWAY SW 562/01CB is a typical 3-needle flatbed.
- Cylinder arm — for hems sewn in the round: sleeve cuffs, trouser bottoms, tubular waistbands. If you hem finished sleeves, you need this. The SPEEDWAY SW 662-01/CB is the cylinder-arm equivalent.
A flatbed cannot hem a closed sleeve. Buying one to do that is the single most common return we see in this category.
Which one do you buy first?
If you only have budget for one, start with the overlock — but for a specific reason, not just because it is cheaper.
With an overlock plus a straight lockstitch you can build a complete garment: the lockstitch does the structural seams, the overlock seams and finishes the knit edges. With a coverstitch alone you cannot, because a coverstitch only hems and topstitches — it never assembles anything.
Then add the coverstitch as soon as you are selling knitwear. A lockstitched t-shirt hem is the fastest way for a customer to spot a homemade garment.
| If you make… | You need |
|---|---|
| T-shirts, activewear, knitwear | Both. Overlock for seams, coverstitch for hems and necklines |
| Woven shirts, trousers, uniforms | Overlock (or a 516 safety stitch machine). Coverstitch optional |
| Jeans and workwear | 516 safety stitch overlock, plus lockstitch and bartack |
| Alterations and repairs | Overlock first; coverstitch only if you hem knit garments regularly |
Tell us what you are producing and we will tell you the configuration — thread count, needle system and bed type — rather than just a model number. Every machine is assembled and tested in Miami before it ships, and our own technicians handle warranty and service. Call +1 (954) 681-3894, English or Spanish.