Where to start? The head of this massage tool is about 30mm. Inside it contains a small rolling probe that presses up against the inside surface of the tool which in turn presses the outside against your prostate. Its like the very end of a finger motioning to come hither and does it with three speeds of operation. The shaft is long enough to find any man's prostate so don't just slide it in till it stops like you can with a Nexus Revo Stealth or several of the higher end massagers available. The rotation motion of the revo is heavenly, but requires far more adjustment to keep it in the "sweet spot" The Senseuelle's vibrator is plenty strong enough to get the job done. I honestly seldom use the vibrating function because the head of it produces such an intense sensation that its not really necessary. I own two fun factory pulsators, a revo and titon from nexus, and two Lelo massage tools. I'm not just trying to talk up a cool new toy. After the countless hours I have taken to research all of these wonderful devices, this I believe is the BEST investment for your dollar! (4 stars because the motor is strong enough to break the drive mechanism that delivers the ******** motion in the tip).