Voltage 3.2 kg per finger, difficulty level is for my little finger, use for over 1 month, very satisfied. Update 07/08/2013 Use since January 2012 several times a week by 100 reps x2 or x3, product quality that can be described. Thanks to him, I could strengthen my two hands (no more atrial level difficulty) and there is little time I was able to go to the next model of 5 kg but I have to switch between the 2 so far before consider use it only model of 5 Kg. For my part, I observed joint pain, and redness occurring due to friction when I apply pressure with the 5 kg (significant after 50 reps), so a board will be moderately Take the model of 4 kg.