The L808WHF19 is a white PP plastic 38-400 child-resistant cap with foam 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 includes a foam liner, which will create an airtight seal when the lid is securely screwed on to the container. 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 38-400 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.