Connector for the Telescope Handle of a Beldray Pet Plus Rubber Head (available on Pet Circle).
This is an approximation of the original with measurements taken by caliper. The connection to the telescope handle is friction-based hence quite tight. You might have to give it a bit of a push with a rubber mallet, just be careful to apply the force straight down as to not break it.
I've printed this in PETG with 100% infill and 0.2mm layer height with surface pattern on concentric. The thread end facing on the build plate with support structure generated around the threading. I figured it'd be easier to remove and the threading is fairly tolerant.
The author marked this model as their own original creation.