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Need to 3D print a size 5 Ring but not knowing how to set length or size of the ring

ZBrush Artworks
#1

Hi, I have a ring to print out but cannot find any tool to allow me to define the unit or length. I cannot find any tutorial, document or instruction which explain how this can be done. I have been searching for weeks so I try to get help here,
Thanks,
Simon

#2

Are you using ZBrushCore or ZBrush?