O-ring screw cap is manufactured from autoclavable polyethylene and polypropylene which forms a positive seal against the rim of the tube to protect against leakage even under demanding conditions. Available in a variety of colors, these screw caps adapt to a range of experiments. Plug caps are suitable for routine laboratory analysis and procedures. Low-density polyethylene plug caps are matches for capless microcentrifuge tubes. Available in a size that accommodates both 1.5 and 2.0 mL capless tubes, they are useful for collecting fractions and mixing reagents. Plug closures are not autoclavable.