Unique design, Tubes will be fastened by the silicagel cushion and wont fall off when the rack being inverted. No noise, no breakage when being shocked or fallen off. It is suitable for various kinds of test tubes and centrifuge tubes with diameter less than 18mm. Racks can be connected for 100 wells or more use. Sturdy and durable material, no distortion under autoclave. Acid and alkali resistance.