You made a great choice, the Thunderhead 100' s are good heads. I' ve been shooting these broadheads for many years and have never had any reason to change. I' ve never had a problem with the rubber o-ring myself. I shoot goldtips and now buy the carbon thunderheads which are the same as regular thunderheads but they include the metal washer that was mentioned or you can just buy those seperate. I also wouldn' t pay the extra bucks for the pro series because i just don' t think there' s that much difference other than looks.