The 73S shaving head and the 70S shaving head are both suitable for the Braun Series 7, but they are not directly interchangeable. The 73S is compatible with all Series 7 models with a 360° Flex head, while the 70S was developed specifically for models such as 720cc, 730cc, 735s, 750cc, 760cc, 790cc and 795cc. Although both belong to the same series, they differ in terms of compatibility and design.