Solid, virgin PTFE, standard taper, joint inserts. For 6467 series stainless steel, flat heads. Top of insert is outside standard taper joint that matches glass standard taper inner joints. Bottom is made with a reverse thread and comes with a PTFE collar and FETFE o-ring for attaching to the flat heads. Top of insert is also machined to accept 7597 joint clips. 100mm Duran® flange o-rings, 7855-880 Capfe or 7855-696 Kalrez, sold separately.