Autosampler Vial Septa. Thermo Scientific™ National Vial Septa are designed for use with 4mL screw-thread vials. Septa for 8-425 Screw Thread Caps are constructed of PTFE, PTFE/rubber, or PTFE/silicone to suit a variety of applications. Combine the inertness of a PTFE coating with the resealability of silicone Thermo Scientific™ PTFE