The assembled cap and septum are very convenient for customers to use. 2mL Standard Opening Vials. Our standard 2 mL vial is 12 mm in diameter, 32 mm in height, 5.5 mm opening. The thread size on this vial is 8-425. Choice of clear or amber glass. These vials are the very best available today for HPLC, GC, LCMS & GCMS.