What is it?
A 4-thread overlock uses two needles and two loopers. It sews a seam and wraps the raw edge at the same time, with an extra line of needle stitching that adds security.
When should you use it?
- Joining seams in garments
- Sewing knits such as jersey and sweatshirt fabric
- Seams that will be under stress, like side seams and armholes
- When you are not sure where to start
What fabrics work well?
Most medium-weight wovens and many knits. On very fine fabrics it can feel bulky — a 3-thread or narrow overlock may suit better.
How many threads?
Four: two needle threads and two looper threads.
What should the finished stitch look like?
Two straight, parallel needle lines on top, with looper threads meeting neatly at the cut edge. The seam should lie flat without puckering or loose loops.
Common problems
- Loops on top or underneath — usually a looper threading or tension-disc issue
- Puckering — check differential feed is at neutral
- Wavy knit seams — avoid pulling the fabric and check your differential feed
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