This is a replacement Tail drive belt for the Align 450 SE, V2 and Sport series helicopters. The belt runs inside the tail boom and is driven by the tail drive gear and transmits the power to the tail rotor shaft assembly. Careful adjustment of the belt tension is required for optimum performance. Having the belt too tight can cause excessive power consumption while running it too loose can cause slipping and premature wear to the belt and pulleys. Package includes one 397 tooth x 2.6mm tail drive belt.