Vicmarc V00676 VM120 Dovetail Jaws 105mm (4")
Designed for mounting bowls by expanding into a recess or clamping onto a spigot.
The sizes indicated on the drawing are when the jaws form a perfect circle, which is achieved when the jaws are 2mm apart. VM120 and VM150 chucks provide approx 48mm of expansion beyond these specified sizes.
I needed jaws that would open about an inch bigger than the standard factory jaws that came with the chuck. These were perfect.