Twin needle uses a sort of a chain stitch on the back of the fabric to connect the two straight lines on the front. At the back of the fabric there is a loop made So it is not as strong as a single straight stitch. In a factory made garment, a single needle seam is considered superior to a double needle seam because of its finish and strength. So if you want a strong seam this is not the one you need to use. The stitches might cave in if you do not get the tension right.