After the eye and the brain, the 10x Loupe (or "hand lens") is the instrument most used by gemologists. It is used to inspect the interior and exterior of a gemstone, and is the primary instrument used for clarity grading of diamonds. This 10x 21mm triplet loupe from Hobby Tool Supply uses 3 lenses to provide a sharp image with little to no spherical aberration/distortion. Thanks to the case's eyelet, the loupe can be attached to a chain or string.