portion 11 fin 26 further comprises a fin root 27 extending perpendicularly from surface 47 and has a generally rectangular body portion 48 having a ridge portion 49 disposed longitudinally thereacross on both sides thereof as will hereafter appear ridge portions 49 respectively coact with and engage slots 41 42 in receptor 30 to provide a snap lock fit when fin root 27 is properly inserted into channel 40 generally rectangular extension portion 50 abuts ridge portions 49 and extends outwardly therefrom portion 50 has a first seat 51 and a second seat 52 defined therein to define a tab of key 53 therebetween each seat 51 52 corresponds to the receptor 30 disposed in registered relationship thereto while key 53 formed therebetween engages the outer surface of motor tube 12 intermediate the receptors 30 and in axial abutment therewith similar connections are made at each of the remaining receptor sites until the desired number of fins have been installed to assemble a rocket fin 26 to rocket 10 as shown in fig6 fin root 27 is passed through slot 36 until seats 51 52 enter into and are secured by corresponding receptor 30 whereupon ridges 49 are by the action of ridges 49 enterring slots 41 42 where they are locked while the exemplary embodiment shown herein employs two finlock ring members 28 it.