The author remixed this model.
As I didn't have the same magnet but only 6x2mm one I recopied the shape and adapted it.
Furthermore I modified the cavity for magnet to put 3 of them max and there is an integrated 5.5mm O-ring at the entry to keep magnet inside without using glue.
I printed it in TPU, which gives some flex to fit magnet and adapt to different tube.
In the FreeCAD file you will find a second version called "short". It is shorter by 10mm to allow to use shorter elastic band.
One picture is the normal version, the other one is the “short”.