Autosampler Vial Septa. Fisherbrand™ Septum for 20mm Crimp Cap. Most septa are laminated on one side with PTFE for high chemical resistance and an inert barrier between sample and carrier material. Pricing and Availability. Thermo Scientific™ 8mm Autosampler Vial Septa. Septa for 8-425 Screw Thread Caps are constructed of PTFE, PTFE/rubber