Hammerhead Fins (Sizers) are designed to match the ball size to the barrel. The type of ball, weather and manufacturers tolerances can all have an affect on a paintball size. To optimize your barrel performance it makes sense to have the right sizer for the ball used that day. HammerHead Fins are 2 in length which is an optimal length based on the amount of air pressure that occurs during the first two inches of a ball being shot out of a paintball marker.