Metal Ball Blue Cobalt Glass Roll On Bottles for Essential Oils, Perfume Oils and Aromatherapy Oils, 5 ml - 7 ml Max Capacity (6) 5ml-7ml Blue Glass Rollon Bottles with Metal Balls and Black Caps for Essential Oils Durable and Easy to Use Metal Ball Roll Ons NOTE: Only use these Metal Ball Rollers with pure uncut oils. Do Not use Metal Ball Rollers with diluted or carrier oils, particularly fractionated coconut oils. This is a high lubricant oil that will force your metal ball to pop out. For these type of oils you should use plastic ball roller bottles. Use with your 100% Pure Essential and Uncut Perfume Oils Refillable and Reusable Metal Ball Roller Bottles