Door sill for a vehicle, sub assembly for a passenger compartment and corresponding realisation method, and double shell false floor

The door-sill has an association unit (11) that associates with a door frame (1) having an inner shoulder (3), and a partial covering zone (12) with an external countershaft partially covering an outer wall of a groove. An integration unit (14) integrates with a fitting unit of a floor pan (90). The partial covering zone protects fixation units of a sealing ring. Independent claims are also included for the following: (A) a sub-assembly of a cab interior of a motor vehicle (B) a method for assembling a sub-assembly.