15-425 black screw pp cap has a 15mm outer diameter, which means it is compatible with vials that have a corresponding neck size and threading. These caps are typically made from high-quality materials such as polypropylene. These polypropylene caps have excellent sealing characteristics and offer good chemical resistance including acids, alcohols, alkalis, aqueous products, cosmetics, and household oils. Polypropylene Hole Caps are known for good impact strength, cost-effectiveness, and pliability.