Polypropylene caps are chemically inert and suitable for most chromatography applications Shop Fisherbrand 8mm PP Screw Seal, Black, Center hole, 8-425 thread, Fisherbrand™ 8mm PP Screw Seal, Black, Center hole, 8-425 thread, Assembled septum Silicone/PTFE white/red,1.3mm thickness,45° shore A Fisherbrand™ 8mm PP Screw Seal, Black, Center hole, 8-425 thread, Assembled septum