This is a replacement for the ear clip of the Plantronics M70 head set. The shape should be quite close to the original clip. It might fit to other Plantronics head sets like the Explorer or the Voyager but I didn't try it. The diameter of the round part it snaps on to is 6.3 mm.
The original broke and the existing models didn't quite fit so well. Therefore I just designed another one. Prints well in PLA and PETG with 100% infill and should be stable enough to last a while.