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 workpieces.

The sizes indicated on the drawing are when the jaws form a perfect circle.  VM90 and VM100 chucks provide approx. 38mm of expansion beyond these specified sizes.  
 
See dimension table for part numbers.