The M1352BK is a black PP plastic 24-400 ribbed skirt dropper assembly with 1 cc monprene bulb and 108mm glass pipette (for 4 oz dropper bottles). Dropper assemblies are composed of a number of parts: the cap, the bulb and the pipette (tube). Dropper assemblies are used with liquids that require precision and intricacy when using the product. Polypropylene (PP) is marked with the resin identification code of 5. PP is less flexible than LDPE, somewhat stiffer than other plastics, reasonably economical, and can be translucent, opaque, or of any color. PP has very good resistance to fatigue, and has an extremely high melting point (320 degrees Fahrenheit or 160 degrees Celsius). This closure fits a container with a 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.