The Rodaviss kit (High Temp PTFE) is a female threaded stopper designed to thread with the glass of a 45/50 joint. The 45mm joint threads with the Rodaviss for added reinforcement while the joint itself forms a leak tight seal. Installation diagram below for further explanation. Here are some of our products that utilize the Rodaviss kit: Chroma Cap Cold Trap Flask Rodaviss SS Trap Adapter   Three piece Rodaviss kit only. No glassware included.   Installation Diagram