For many years I didn’t know that these two are different stitches 😂
The main difference – the position of the working thread while making the embroidery. As you work Outline stitch from left to right, always keep the working thread above the line of stitching. And when you embroider a Stem stitch from left to right, keep the working thread under the stitching line.
The other difference that you may notice – the direction in which the “rope” of the stitch is twisted. For this reason, sometimes it’s better using Stem stitch and sometimes – Outline stitch. If you are not sure which stitch will make a more beautiful curve and is more suitable for your design – try to make the same curved line with both and see which you like more.
Watch this short video tutorial where I demonstrate the difference between Outline stitch and Stem stitch.