Open the top of this beautiful diffuser and Apply a couple of drops of your favorite essential oil to the wool felt pad to experience the benefits while driving. This style of diffusers easily clips to your vehicle's air vents, where the air flow comes through holes in the back of the diffuser to distribute the scent. The diffuser is 316L Stainless Steel Hypo allergic, Lead and Nickle Free, with an outside diameter of 30mm (1.2"), and vent clips that are 30mm (1.2") long. Vent clips are metal. Comes with 4 different colored wool felt pad inserts. Insert colors vary.