These jaws are used for expansion into small recesses and for firm holding of fine spindle work, such as earrings, chess pieces, etc. They are ideal for turning salt and pepper shakers. To turn very small articles, the jaws can be unscrewed and the backing jaws only can be used.
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.