Stem stitch vs split stitch
Stem stitch and split stitch use the same holes in the same order. The one difference is where the needle comes up: beside the last stitch for stem stitch, through the middle of it for split stitch. That small change gives two quite different lines.

The differences
| Stem stitch | Split stitch | |
|---|---|---|
| Looks | A twisted rope of slanted stitches | A fine, flat line like a tiny chain |
| The needle comes up | Beside the last stitch, with the thread held on the right of your direction of travel | Through the middle of the last stitch, splitting its strands |
| Strands | Any number: 2–3 for most lines | An even number, 2 or 4, so it splits evenly |
| On curves | Excellent | Good |
| The back | Small backstitches, half a stitch long | The same: small backstitches, half a stitch long |
| Best for | Stems, flowing outlines and script lettering | Fine lines, lettering and edges under satin and long and short stitch |
Which to use
Use stem stitch for flowing curves and plant stems, where a raised, rope-like line looks best. How to work stem stitch
Use split stitch for fine, smooth lines and small lettering, and as the edge under satin or long and short stitch. How to work split stitch