screw cap septa Aijiren 10ml GC Headspace Vials. Headspace Vial. 10mL & 20mL screw neck ND18 rounded bottom headspace vials with matched 18mm magnetic precision screw metal caps, 17.5mm PTFE/silicone septa. Use: Liquid 20mm AL Crimp Cap & Silicone/PTFE Septa, Kit, flat bottom, 100/pk. Vials, 10mL Headspace vial w/ 20mm AL Crimp Cap & Silicone