Septum rubber | Sigma-Aldrich Pricing. 854984. black polypropylene hole cap, thread for 8-425, PTFE/rubber septum, for use with 11.6 × 32 mm vial (standard opening), pkg of 1000 ea. Pricing. 854987. black polypropylene hole cap, thread for 13-425, PTFE/red rubber septum, for use with 4 mL vials with 13-425 thread, pkg of 100 ea.