a vane , that can be mounted to a projectile to provide stability of flight , without substantially degrading speed due to added weight and / or causing clearance concerns . the vane is approximately one inch long and 0 . 4 inches high with a front - edge and a back - edge that meet at a point . the back - edge arcs down towards the base of the vane while the front edge degrades in a substantially linear fashion to the base of the vane .