The IMM Draw Size plugin allows you to set a specific size in millimeters for an IMM Part. After setting the desired size and clicking ‘Set IMM Draw Size’ the draw size will be updated for the current model. The next IMM part that is drawn out while holding ‘CTRL’ will be the precise size. (Note: The IMM Draw Size plugin will always use the longest dimension for the selected IMM part when calculating the size.)

This plugin has had limited testing and could contain potential bugs; please save your work before using.

Plugin can be downloaded at:
https://pixologic.com/zbrush/downloadcenter/zplugins/