20mm Crimp Top Aluminum Caps with Septa – HPLC Vials 20mm crimp top aluminum cap material is a metal aluminum cover. The design with a 9.5mm hole in the center of the cover can be used for headspace analysis. LLG-Headspace Crimp Neck Vial N 20 5ml 4008285 | Lab Unlimited Outer Diameter: 21.7mm. Outer height: 38.2mm. Clear Flat bottom