Headspace Vial. Products Often Purchased with 20 mL, 18 mm Headspace Screw-Thread Vials, Clear, 100-pk. Vial Storage Rack for 6, 10, or 20mL Headspace Vials, 36 Vial Capacity, Polypropylene, ea. 18 mm Magnetic Screw-Thread Headspace Caps and Blue PTFE/Silicone, 1.5mm thick Septa for SPME, 100-pk. 18 mm Magnetic Screw-Thread Headspace Caps and