This is a replacement part for the strain relief in an xlr plug.
 

Some XLR Plugs have crimped strain reliefs which can not be reused (e.g. “Rean” branded xlr plugs, as seen in the bottom part of the last picture). This replacement part is the typical kind of strain relief which can be reused.

v2 is the version you can see in the photos and seems to fit well.
v3 has coarser teeth to grip the cable. I didn't test it yet.

Print standing upright with a brim (trim your brim to be easily removeable by hand).