Bio Plas® brand screw-cap microcentrifuge tubes offer extraordinary strength, safety and reliability. They allow users to perform procedures that simply can't be done with other tubes. Spin it, store it, transport it (even by air). Boil it, irradiate it, immerse it in the vapor phase of liquid of liquid nitrogen -- it'll stand up to the test. Inside the screw cap, our ethylene propylene O-Ring forms a secure, leakproof seal. The cap's square threads won't strip -- and they're on the outside of the tube, so you minimize the risk of contaminating your sample -- or letting it contaminate you.