A quick video on the 3 most popular stitches on sergers, the 4 thread (2 needle, 2 thread), 3 thread (2 needle,1 thread), and the 3 thread (1 needle, 2 thread).
The ones with 2 needles are much strong seams, but slightly less stretch than the 1 needle stitch.
The 4 thread uses the most thread (bulk), the 3 thread 2 needle (slight less bulk), the 3 thread 1 needle (least bulk).
I use the 4 thread mostly, but I make most of my stuff for men, which are much harder on clothes than women.
The 3 thread 1 needle, I use on swimwear. but also topstitch it.
