Screw cap, headspace, steel, magnetic cap, PTFE/silicone septa (top white, bottom blue), 18 mm, 100/pk. Cap size: 18 mm – Aijiren Headspace Crimp Top Vials. Cap, crimp, headspace, with septa, 20 mm, silver aluminum cap, certified, molded PTFE/butyl septa, 100/pk. Cap size: 20 mm Nd20 Long Neck Headspace Vials