Hammerhead Fins (Sizers) are designed to match the ball size to the barrel. The type of ball, weather and manufacturer’s 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. Precision machining - Made in USA.