Headspace Screw-Thread Vials, 18 mm - Restek Vial Storage Rack for 6, 10, or 20 mL Headspace Vials, 36 Vial Capacity, Polypropylene, ea. 18 mm Magnetic Screw-Thread Headspace Caps and PTFE/Red Chlorobutyl Septa, 1000-pk. 18 mm Magnetic Screw-Thread Headspace Caps and Blue PTFE/Silicone, 1.5 mm thick Septa for SPME, 1000-pk.