See the Youtube video for the features of the Vicmarc shark jaws:
Shark Jaws have serrated inner and outer jaw surfaces. These extended jaws provide an aggressive hold. they hold cylinder spigots much more safely than standard jaws. They are much easier and provide vastly better grip than traditional jaws used to turn long work pieces.
These jaws should not be used to grip the bowl on a finished surface.
The sizes indicated on the drawing are when the jaws form a perfect circle. VM120 and VM150 chucks provide approx 48mm of expansion beyond these specified sizes.