A 12mm inductive proximity sensor mount for the Cetus 3D, e.g. sold by tinyfab.
It is inspired by https://www.thingiverse.com/thing:3001088 but mounts to the side of the extruder motor as newer versions of the Cetus 3D seem to be missing the mounting plate at the bottom of the assembly.
It might need a bit more clearance for the washer but in principle it works.
Please contact me if you need a different license.