Bi-layer include silicone and PTFE. Silicone septa for multiple injections. PTFE-lined screw cap for organic samples. Screw caps provide an inert, airtight seal and direct puncture-access to samples with a syringe needle. Rated 4.8 /5 based on 509 customer reviews. 9mm cap hplc cap pp cap pp cap for hplc screw cap. Free Sample Get Price.