Also (wrongly) known as an Andean plying bracelet this is a great way to make a 2-ply yarn from 1 bobbin of singles.
This video is part of a Hilltop Cloud course called Spinning with a Purpose.
It's an online workshop that you can access at your own pace, and with online support throughout. Find out more here-
https://www.hilltopcloud.co.uk/online-courses.html