The lap sliding fit in cast restorations is provided by:

The gingival bevel serves the following purposes:​ Weak enamel is removed. If the gingival margin is in the enamel, it would be weak, if not beveled, because of the gingival inclination of the enamel rods.​ The bevel results in a 30-degree metal that is burnishable (on the die) because of its angular design. Bulky 110-degree metal along an unbeveled margin is not burnishable.​ A lap, sliding fit is produced at the gingival margin. This helps improve the fit of the casting in this region. With the prescribed gingival bevel, if the inlay fails to seat by 50 µm, the void between the beveled metal and the gingival bevel on the tooth may be 20 µm; however, failure to apply such a bevel would result in a void (and a cement line) as great as in the failure to seat. Sturdevant operative dentistry 7th Edition, Page No:e106