The specification includes 11mm, 13mm, 18mm, 20mm aluminum crimp caps and magnetic screw thread caps as well as 8mm, 13mm, 15mm, 18mm, 20mm, 22mm, 24mm plastic screw caps with PTFE Silicone Septa. These caps are often used in laboratory chromatography and ideal for assembling headspace vials, HPLC vials, Gas vials, EPA vials, VOA vials etc.