Ready-to-wear Ts are hemmed with a serger. To duplicate the look with a regular sewing machine all you need is a twin needle and two spools of thread and a bobbin. The twin needle is a specialty-needle for the machine. Twin needles are two needles mounted on one shaft.
When shopping for a twin needle, look for a package marked Twin Needle/Stretch in either 2.5 or 4.0 mm. Stretch needles have a ball point and a specially designed eye and scarf (the part of the needle just above the eye) that prevent skipped stitches.
The numbers 2.5 and 4.0mm refer to the distance between the needles. The larger the number, the greater the distance between the needles. Remove the presser foot and test the opening in the throat plate to see if it will accept the wider needle set-up. You may need to change the presser foot and the throat plate.
Our finished sample shows two colors of thread in the upper threading, a third in the bobbin. Usually you will use three matching threads. Thread the upper machine with one spool at a time, making certain that each thread passes through tension disks. Position the spools on individual spool pins with one spool (green thread) feeding off the top (or left) and the other spool (red thread) feeding off the bottom (or right). Install bobbin as usual.
Working with the inside of the T-shirt facing up, turn up the cut edge the desired amount for the hem; press.
With the outside of the T-shirt facing up, pin hem in place. Using a stitch guide to keep stitching straight, sew to make the hem, removing pins before you sew over them.
The single bobbin thread catches both top threads and zigzags between the two rows. Using the stretch needle builds in “give” in order that the hemmed fabric can be stretched without fear of popping hemstitches.