10-425 Black Polypropylene Hole Cap with Red PTFE/Silicone/PTFE 0.040" Septa with Slit. Polypropylene Screw Thread Vial Caps are available as unlined hole caps or solid top caps. Known for good impact strength, these vial caps are both durable and cost effective. Hole caps are sold with standard or large opening with a variety of color options.