Most main seaming, sometimes known as double locked stitch.
This two thread chain stitch formation is used for seams where elasticity,
strength and continuous sewing are required, e.g. Jeans.
It is formed by two threads, one used in the needle and the other, an under
thread carried in a looper. This stitch is formed by the needle thread being
interlooped with the under thread. This stitch produces a very strong seam
with some extensibility.
As in all chain stitch formations, two thread chain stitch construction seams
should be secured at the seam end, via stitch condense, tacking or inclusion into
another seam to eliminate the danger of running back or unraveling of the
two threads.