A twin needle can be used to make really neat hems at cuffs and bottom edges of blouses, pants and dresses. Especially for stretch fabrics it is brilliant because it finish of the hems leaving them stretchable.
Thread your sewing machine with two threads and the bobbin thread as normal. Be sure to make a test to check if your tension on the sewing machine is set correct.
Use a stitch length at minimum 3-3.5 or a little more. It provides the finest and most professional results.
Fold your seam allowances and stitch from the right side – make sure you have a little extra seam allowance. This makes sewing easier and you can always trim down the excess fabric afterwards.
When stitching you get two parallel stitch lines exactly next to each other and a zigzag stitching on the wrong side which makes the hem stretchable.
Most people use the twin needle like this for hemming, but it is also good for making beautiful neck edges and other kind of finishes for ribbing where you want to lay down the seam allowance on the clothing.
Instead of making your topstitching along the ribbing as you normally would do, press the seam allowance away from the ribbing and stitch right in the middle of the seam. See photo.
This gives you the nice little different finish as you can see at the photo and the seam allowance will be held neatly in place too.
Simple trick but really nice to look at.