Alvin linen testers are basically inexpensive microscopes. The original purpose of a linen tester was to observe thread patterns in determining thread count. They were also used for the inspection of letter quality and checking the dot image of halftones in the printing industry. A linen tester is 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. Choose from glass lenses with either plastic or brass folding frames. We also have LED magnifying glasses, jeweler's loupes, and dome magnifiers.