Vials, Headspace, Crimp Top, Glass. Clear. 20ml, 20mm Serum Finish, 22.5x75.5mm outer dimensions, Special Top and Flat Bottom for use with SPME Caps. Clear. 20ml, 20mm Serum Finish, 22.5x75.5mm outer dimensions, Special Top and Flat Bottom for use with SPME Caps.