The stem cap includes four pieces of the silicone-made product. They are perfect for pre-packing the glass aromatic stem tubes to be used throughout the day. The user can also use these stem caps to protect skin, pockets and other containers from the hot glass. The silicone is manufactured from the high-quality, food-grade material, which means it’s not toxic. The stem cap pack is compatible with the Air-Frosted Glass Aroma Tubes, Air Glass Aroma Tube, and Air-Tipped Glass Aroma Tubes. This pack is designed to be compatible with the Arizer Air and Air 2, although the standard size will also make it possible to mount it with other glass tubes.