Step Jaws, designed by the famous Australian woodturner and author Richard Raffan, are used for holding a range of spigot sizes with minimum jaw movement and without the necessity to change the jaws. Boxes are easily turned using the step jaws. The bottom can be turned by holding the rim without leaving unsightly pressure marks.
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.