4ml (1 Dram) Cobalt Blue Glass Roll-on Bottles with Metal Roller Balls - Refillable Essential Oil Containers for Aromatherapy, Perfume & DIY Blends (Pack of 720) - Perfect for Travel, Gifts & Home Spa Use

These are pretty but much smaller than my usual 4 ml bottles. Perhaps the glass is that much thinner allowing 4 ml to fit into a bottle that is 1/2 the size of my normal 4 ml rollers. (?)One of the bottles was broken when it arrived and after a couple of weeks of use of one of these the roller ball fell out. With my experience with the 1 ml clear roller bottles from this same manufacturer I will not buy from them again. I strongly suggest finding a different manufacturer.These are exactly what I needed, and so far are working as expected.The steel Roller ball fall out on some!Lids sometimes screw on awkwardly!Size works great for travel and give-aways-just wish those steel balls could be reconfigured to stay tightly in place!handy.They work great! I use with my essential oils. Just wish they were packaged in a box, other than that no complaints.These are great . I use these for samples.Very convenient to carry and great looking bottles. They do not leak and break.