100ML Boston PET plastic are round bottle with 20-410 neck finish. The Boston round bottle is distinctive in its classic shape. Characteristic of the boston round are its rounded shoulders and rounded base. Polyethylene terephthalate (PET) is marked with the resin identification code of 1. PET is of the polyester family and has high clarity, good chemical resistance, high impact resistance, and medium rigidity. PET is also light-weight and is used for Wide Range of Cosmetic , Skin Care and Personal Care products. 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 item has a 20-410 neck finish. The first number refers to the diameter (in mm), and the second refers to the closure depth, style and thread. This container can be paired with a closure or pump of your Choice from our Caps and Closure Section of our Website. The Bottle Neck Height is Reduced to make it Suitable for Spray / Treatment Pump or Disc Top Cap hence Avoid Using Flip Top Cap on it