The J072 is a 16 oz clear PET plastic square firenze jar with 89-400 neck finish. Firenze jars are square shaped jars with wide mouths, round shoulders, rounded base, and rounded corners. This jar is made of polyethylene terephthalate (PET). PET is of the polyester family and is semi-rigid, and very light-weight. It has high clarity, is strong and impact-resistant. It has a good chemical resistance. Avoid using PET containers to store products that contain essential oils greater than 5% or fragrance oils greater than 15%. If your oil percentages exceed these respective levels, please consider using glass. This jar has a 89-400 neck finish, and will fit closures with the same finish. The first number is the diameter of the container's opening (in mm). The second number refers to the thread/style/depth of the closure's skirt.