I like extruded clays because of the control you have over size and shape. I’ve been afraid the bangles would be weak. These are not! In fact I was asked if they are made from wood
(Great way to use polymer “mud” under those veneers too.)
Decide whether you want to extrude the colors you will use or extrude a “base” you will cover.
Tools needed: Extruder, 2 dies which will create extrusions that fit together (like those shown), polymer clay conditioned to be pushed through the dies. An oven-safe armature to shape the bangle to the size you need while it cures.