These closures are specifically designed for diagnostic applications, and offer all the advantages of an aluminum seal and stopper with the convenience of a screw cap. The unique combination of a stopper and screw cap ensures excellent sealing characteristics, making them ideal for liquid reagents. You can access sample contents using a syringe through the stopper or with a pipette after removing the screw cap. The closures are available in black, white, red, blue and yellow polypropylene closures. Tolerances in the stoppers are maintained to .005. Autoclavable.