The magnetic screw caps can be used for headspace as well as for SPME. Type of Cap: Magnetic Precision screw cap, Closed screw top 20ml headspace vials with writing space manufacturer Products name 10-20mL 18mm Screw Thread Headspace ND18 Dimension 18mm Cap Color Silver Septa details White, Red, Blue, 1.3-1.6mm thickness. Material Aluminum for Cap,