Uses of the roller balls are generally with glass bottle roll-ons. Sometimes the roll-ons can also denote perfume bottles. This roller ball assembly has a metal casing which keeps the roller ball from falling out. The metal casing of this product can withstand concentrated essential oils and fragrance oils. Essential oils are long believed to be some of the best cures for ailments. From sore muscles to headaches to nausea and just about anything in between. Roller bottles have become the preferred way to apply essential oils because they allow the right amount of oil to be applied to just the right area without any extra mess and are easy to mix into carrier oils.