This is a 2.7oz/30ml PET Cosmo Round Bottle and has a 24-410 neck size. The cosmo round, also called bullet round and imperial round, is characterized by its tall and slender build with steeply rounded shoulders. PET has high clarity, good chemical resistance, high impact resistance, and medium rigidity. PET is also light-weight and is used for products containing essential oils. 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. Sold by the case (100 bottles per case).