Which of the following is not required for retention of cast gold restoration?
Retention form is attained by

Creating a maximum of 2-degree occlusal divergence of the vertical walls,
Accentuating some line angles, and
Extending the lingual surface groove to create an axial wall height in this extension of at least 2.5 mm occlusogingivally.

Sturdevant Operative Dentistry 7th edition page e110
Cavosurface bevel
Parallel walls
Beveled axiopulpal line angle
Undermining dentinal walls