Sep 23, 2019 · These caps are manufactured from high quality polypropylene and fit all of the 8mm screw top vials. Features: *Compatible with 12x32mm 8mm screw cap vials *Both Pre-slit and No pre-slit septa are available *PTFE/Silicone/PTFE septa are autoclavable and offer excellent resistance to coring *Pre-assembled caps save you time and reduce contamination