The L353WHH56 is a white PP plastic 33-400 child-resistant cap with a heat induction seal (HIS) liner. Child-resistant caps are equipped with a locking mechanism that requires additional effort to open. To be designated as "child-resistant" these caps have undergone the requisite evaluations of a regulatory agency. This closure comes with a heat induction seal (HIS) liner, already placed inside the cap. An HIS liner is a metallic disk that provides an airtight, tamper-evident hermetic seal when an appropriate heat induction sealing process is applied. This liner can work with LDPE, MDPE and HDPE containers only. For more information on heat induction sealing and available machinery, please read our article. Please read 5 seals and how they make perfect liners for your container for more information on liner types. This lid is made of polypropylene (PP), which means it has a high heat tolerance level and an excellent resistance to fatigue. This closure fits a container with a 33-400 neck finish. The first number refers to the diameter of the container's opening (in mm). The second number refers to the thread/style/depth of the closure's skirt. Please read 5 seals and how they make perfect liners for your container for more information on liner types. This lid is child-resistant making it ideal for packaging pills or other potentially hazardous products.