MBP Screw Caps for Screw Cap Tubes by Molecular Biology Products are polypropylene caps with a chemical-resistant O-ring for a tight seal that limits evaporation. Caps fit 0.5 mL, 1.5 mL and 2.0 mL screw cap tubes in clear, blue, green, orange, red or yellow for color coding, and blue caps fit 5 mL and 10 mL tubes. Caps are packed 500 per unit, 8 units per case.