8X linen tester folding magnifier features dull black, anodized-finish brass folding frame and glass lens. Great for observing thread patterns and determining thread count. Also used for the inspection of letter quality and checking the dot image of halftones in the printing industry. Linen testers are ideal for student geology or biology lab projects. These folding magnifiers can also be used for home/hobby use such as stamp and coin collecting, quilt making, sewing projects, electronics, and more. Approx. size open: 1/2" x 1/2". 8X magnifying power. Inside edge of base has easy-to-see white filled 1/8" graduations. Includes case.