This design helps damp the vibrations of the arms holding the hotend box for the FLSUN delta printers (e.g. QQ series, Q5; 6 mm in arm diameter). It has the following major advantages as compared with other similar designs:

1. it doesn't slip along the arms even after use for a long time (slipping is a well-known problem for similar designs);
2. it fits rubber bands of any size, because you could put in different amount of (or no) spacers to adjust the spacing of the hooks on an arm;
3. less interference with the printer cable because the two ends of the clip/hook assembly on an arm smoothly merge onto the arm surface;
4. it confines only the degrees of freedom that need to be fixed while leaving others to function as needed;
5. it's slim!

This is the latest version after many iterations of tests (as shown in one of the pictures). It's been working well for me for some time so I thought maybe it's about time to share it here.

Installation steps: (see pictures)

1. clip on the spacers at the properly measured position on the arms (same distance from the joints); the size and amount of the spacer(s) depend on the length of your rubber bands;
2. clip on the hook clips;
3. rotate the hook clip one by one so that the hook is pointing to a direction perpendicular to the plane of the joint ring holder of the arm;
4. hook on the rubber bands in whatever configuration of your preference.

Hope this helps (mostly for removing the vibration noise from the arms and for stabling the print quality).

Further notes about assembly/print preparation:

1. each arm needs two "arm_clip_rubberband-half.stl", one of which could be printed in mirror mode for better looking although you don't need to do so (the mirror print) because the hook position is by design aligned well with the axis of symmetry;
2. the two stl files for the spacers are different only in length; choose whichever fits your rubber band; for each arm you could use more than one spacer (sitting next to each other) if your rubber band is long.