Designed for compound archers shooting long distance field and target archery. Parallel designed shaft has three different spines, with a more flexible center Red Zone and stiffer front and back sections. This manages how an arrow flexes in flight to deliver pinpoint accuracy. Will not take a set like aluminum core arrows, and will maintain initial spine for several seasons. Straightness tolerance: +-.0015", Weight tolerance: +- 1 gr. Available in sizes 400 (8.7 GPI), 450 (8.1 GPI), 500 (7.6 GPI), 550 (7.2 GPI), 600 (6.9 GPI). All components sold separately.