The L251B is a black PP plastic 89-400 smooth skirt unlined lid. 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 89-400 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.