The washer seal secured in the top of the cap ensures a positive leakproof seal, time after time, keeping the integrity of the small sample under even the most adverse conditions. The flat-top cap provides a writing surface and can be used with automatic capping machines in packaging industries. Tamperproof screw cap with washer seal and flat top is molded with a deep internal lip that fits snugly against the interior wall of the tube. It will prevent the contents from coming in contact with the seal or threads, thereby reducing the chances of sample contamination. The cap's high profile facilitates manipulation, especially in aseptic procedures. All tubes and closures are manufactured in a clean environment. This series of tubes are available either plain or with printed graduations and a white marking area for sample identification. Perfect for cryogenic work. Non skirted tubes can be centrifuged up to 20,000 x g. Skirted tubes can be centrifuged up to 17,000 x g. Will withstand temperatures from -196C to +121C.