These are 100 pieces of pre-cleaned microscope round coverslips with 18mm diameter in factory-sealed box. They are manufactured under the strict guidelines established by ISO 9001: 2000 Standards. Features & Specifications: Superb flatness uniform distortion-free surface Non-fogging, non-sticking and no bubbles, scratches or striations Dimension: 3/4" (18mm) in diameter Thickness: 0.006" (0.13 - 0.17 mm) Material: glass Quantity: 100