The unique design of this ring by Rocks Off means that it creates both external and internal vibration. Unlike most vibrating rings, the bullet in the 4US is positioned vertically - this allows for bettter contact with the clitoris and actually works with the natural movement of bodies during sex. The ring is shaped so that rather than flowing around the ring, the vibration is interupted and flows into the penis (or dildo). It provides excellent, strong clitoral stimulation for a female partner and actually allows her to feel the vibration internally through her partner's penis! The 7 speed vibe is removable and runs on one 1.5 volt battery (one included). The entire unit is completely waterproof. 4US is made of 100% silicone. It is phthalate, latex and solvent free, completely inert, and non-porous. Cock ring will stretch from 1.25"/ 3.2 cm in diameter to 3"/ 7.6 cm in diameter. Vibrating portion is 2.5"/ 6.5 cm.