DuoClick™ Two Position Screw-Cap Plastic Culture Tubes feature a unique screw closure system. DuoClick™ tubes completely eliminate the excess force, splashing and general frustration of traditional snap-cap culture tubes. The advanced cap design includes two distinct positions for aerobic and anaerobic culturing. Just rotate the cap 1/4 turn to the first click to secure the cap in the aerobic position. Or, rotate it another 1/2 turn past the second click for a leakproof, airtight seal for anaerobic culturing. DuoClick™ tubes are available gamma sterilized, with screw caps attached, and in 20 bags of 25 culture tubes, 500 per case. Polypropylene tubes can be centrifuged at up to 4,000xg. Aerobic culturing at first click. Anaerobic after second click. They have printed graduations witth flat, markable screw-cap.