These are 100 pieces of 18mmx18mm pre-cleaned microscope square coverslips 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 Dimensions: 3/4" x 3/4" (18mmx18mm) Thickness: 0.006" (0.13 - 0.17 mm) Material: glass Quantity: 100