external spool stoper

When i was about to use the external spool holder for the first time i made sure to understand how properly mount and feed the filament into the proper PTFE tubing. But that wasn't issues i was expecting until i watched a video of "how to" and it was cautioned of what may happen if the filament spool vibrated off of the external spool holder and fell off due to the diameter difference between the external spool post and the spool inner circle diameter, as well as the small lip on the end of the external spool post. So i was printing a project at the time and did a DIY with a piece of cardboard since i was unsuccessful in finding a design that fit my needs specifically, hence what my design is intended for specifically the type of external post for the Bambu Labs P2S 3D printer.I figured a simple and straight forward design would be appropriate.