Threaded back stitch
- Double threaded back stitch

Threaded back stitch consists of a foundation of ordinary back stitch with either one or two additional threads woven back and forth under the back stitch. If a single thread is threaded, the line has a wave effect; if two threads are used the line of back stitch has a scalloped effect on both sides. Some authors call this latter version double threaded back stitch.
It is often used for outlining shapes or as a border; each component can be worked in a different thread or colour to create different effects.
Method
Work a foundation row of back stitch.
Using a different thread, come up at the end of the back stitch. Slide the needle under the back stitch without piercing the fabric.
Starting from the same side of the back stitch line, slide the needle under the second back stitch.
Continue passing the thread back and forth under the back stitches.
Take down the needle at the end of the back stitch.
A second thread can be worked from the same starting point: slide the needle under the first back stitch in the opposite direction from the previous threaded line.
Now pass the needle under the second back stitch. The second threading fills in the spaces left on the first threading so that the stitch is symmetrical.
Work the second threading alternately back and forth.
Take the needle down at the end of the back stitch.
1st row: back stitch
2nd row: (single) threaded back stitch
3rd row: double threaded back stitch

Common uses
Embroidery Techniques
References
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Jennifer Campbell, Ann-Marie Bakewell, Guide to Embroidery Stitches (2004) , p.123
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Betty Barnden, The Embroidery Stitch Bible (2003) , p.42