20 mL vial PTFE cap green | Sigma-Aldrich Product Description. SDS. 27021. black polypropylene hole cap, thread for 20-400, PTFE/silicone, septum thickness 1.9 mm, for use with 22 mL vial, pkg of 100 ea. Pricing. 27022. black polypropylene cap, thread for 24-400, PTFE/silicone, septum thickness 3 mm, for use with 20, 40, or 60 mL vial, pkg of 100 ea.