Summary

This lets you take a cheap optical endstop and use it as a filament runout sensor. The optical sensor just slides inside, and there is a hole for the filament to pass through, although you may want to enlarge a bit with a drill after printing. For mouting, it has two bolt holes and is designed to fit on a 2020 frame.
There is a step by step video on how to configure your printer to use this here:
https://youtu.be/jh6CV-C6G_U