These special 25 mm extended jaws are designed to act like a pin chuck - expanding into a pre-bored hole.
This is an especially useful technique for free form edge bowls. A real big advantage over pin chucks though is that you don’t have to bore to an exact size: any size between
the minimum and just under the maximum expansion will do.
The longer jaws allow for a very powerful spigot grip for all smaller work like lace bobbins (up to 6” in length) and delicate pots etc. The jaws also have a dovetail to mount small bowls (up to 6” diameter).