16mm triple square socket with a 1/2" drive, also often called a 12 point or xzn socket. The service manual refers to it as tool number 2567 and/or 3357.
Applications where it is needed:
- Mk5 and Mk6, R32 and Touareg only:
- removing the rear calipers when changing brake pads or rotors.
- VW, Audi, and Porsche Transmissions that have a tamper proof drain plug, it is needed to remove the drain plug when changing the transmission fluid.