Jun 13, 2022 · In the same way, some key features of pre-slit septa are that it can be Pre-slit I or +. It can be pre-slit PTFE or Silicone septa. Usually, its diameter measures 8mm to 22mm with a thickness of 1mm, 1.5mm, and 3mm. Most of which are made of either PTFE or silicone material. Again, pre-slit septa in vials aid in piercing easily.