my trainer says that the 2 first knuckle,i don´t now the english word for them ,but the "pointfinger"..(lol) and the middelknuckle,is the strongest knuckle.and its altso important that when you make a fist,your underarm and hand isnot bended in anyway.(i hope you know what i mean).that will cause less damage to your wrist,and your little finger,and ringfinger.Karate guys also do it that way. and i works for me.