9mm PP Cap with Septa--Aijiren Vials for HPLC/GC. Aijiren’s septa for 24mm screw closures uses natural-color Silicone and PTFE. These Septas have a diameter of 22mm and a thickness of 3mm, which are consistent with the size of the Cap and can be placed between the Vial and the Cap to isolate the air and the.