This is a left ear back piece replacement for Sony 7506 headphones. It allowed me to replace the original cable with 3.5mm stereo socket and use any audio cable with 3.5 mm connector on each side or Bluetooth dongle with an adapter.
It has 6mm hole to screw in a small socket.

Printed with PLA with supports. All of the mess from supports is inside and is invisible, when mounted.
With my printed I added -0.1 mm horizontal expansion. Layer height 0.2mm with 0.3mm nozzle