creating a press fit connection between the inner surface 74 and outer surface 76 of the annular fin 72 and the inner wall 66 and outer wall 68 of the annular groove 64 another method is used for embodiments of the piston 34 containing thread 82 on the annular fin 72 or thread 70 in the annular groove 64 in this method the second edge 80 of the annular fin 72 is placed in the annular groove 64 and the fin 72 is threaded into the groove 64 thereby connecting the annular fin 72 to the piston 34 both of these methods may be used with pistons of any type including cast forged composite and mechanically joined as the annular groove 64 may be easily and expeditiously machined into the crown interior surface 59 of any piston 34 another method of the present application shown in fig5 consists of creating the annular fin 72 as an integral part of the piston 34 in the process of machining the piston 34 and creating the crown interior surface 59 the annular fin 72 containing the inner surface 74 the outer surface 76 and the first edge 78 that extends from the crown interior surface 59 and that is integral with the piston 34 is formed this method may be practiced with forged pistons by simply altering the machining process currently used to create the crown interior surface 59 of forged pistons 34 the annular fin 72 may also be made integral with the piston 34 via a method that includes inertial welding in such a method either the annular fin 72 the piston 34 or both.