Headspace Glass Vials & Headspace Caps. Vial kit, crimp top, headspace, clear, 20 mL, silver aluminum caps with safety feature, certified, flat bottom, molded PTFE/silicone septa, 100/pk. Vial size: 22.75 x 75 mm (20 mm cap) AG . $140.00. Cap Color Silver with Safety Feature Cap Material Aluminum Cap Size 20 mm Certified Yes Glass Tint