18 mm Magnetic Screw-Thread Headspace Caps and Blue PTFE/Silicone, 1.5mm thick Septa for SPME, 100-pk. 18 mm Magnetic Screw-Thread Headspace Caps and Red PTFE/Silicone, 1.9mm thick Septa, 100-pk. 18 mm Magnetic Screw-Thread Headspace Caps and PTFE/Red Chlorobutyl Septa, 100-pk. 23085. 22 x 45 mm. See full list on restek.com