The most common version of the Austin-Healey overdrive drain plug does not have a standard hexagonal head. Instead, it is a large, flat circular plug with six notches (slots) cut into its outer perimeter.

• The Tool:The wrench or socket features six corresponding lugs (teeth) that engage perfectly with these notches.
• Purpose:By engaging all six notches simultaneously, the tool distributes torque evenly, preventing the “mangling” or “rounding” that occurs if you try to use a hammer and punch or a pipe wrench.

On many Healeys, this plug is accessed from underneath the car, though some owners use the interior transmission tunnel access hole (under the carpet) for checking levels.