Note:
Form A with full ball is used when a clean, polished contact surface is required. Surfaces which are not flat and parallel can be firmly clamped or supported with Form B with flattened ball, the movable ball can adapt itself up to 9°.
Drawing reference:
Form A: full ball
Form B: flattened ball
Form BV: flattened ball non-rotating
Form F: flattened ball diamond grip
Form FV: flattened ball diamond grip non-rotating