Aijiren’s Magnetic Precision Screw Metal Cap is 8mm in size, which is very suitable for sealing gas chromatography. 8mm GC-MS vials types-LC MS Vials. 6-20mL GC Headspace Vials 8-60mL EPA Storage Vials HPLC Syringe Filters. Screw top vial kit, 2 ml, 8mm opening, amber, black cap, PTFE/silicone septa, 100/pk GC