These Jaws allow better access between the chuck body and the rear of the workpiece. They are also very practical when pre-turned workpieces or long workpieces have to be refastened. For example, when turning serviette rings or remounting rough turned work.

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.