Microscale, single-neck, round-bottom reaction flask with outer joint externally threaded to allow an O-RING-CAP-SEAL connection with mating male joint. This type connection eliminates the need for clamps while offering the positive leak-tight seal of ground glass. Supplied with threaded cap with hole, one PTFE-faced silicone rubber septum and one O-Ring. Available with externally threaded side port which is also supplied with cap, septum, and O-ring.