The secondary flare is necessary for class II cast gold inlay preparation for several reasons, but basically the direction of the flare results in:

Secondary flare: It is a flat plane superimposed peripherally to the primary flare. Advantages are: Secondary flare ensures cavosurface margins to extend into embrasures (self-cleansing area). Permits easy burnishing and finishing of the restoration. Produces more obtuse-angled and stronger cavosurface margin. In class II cast gold inlay, proximal box should have flares so as to have the metal of 30-40° which is burnishable.