This new 'large' training set will fit the Honey Bee King, Cool and Belt-CP, Trex 450s, 450se, Walkera 22e,36#,60#,68#,76#...It's balls are made of solid foam and the rods are 33cm in length (each). It helps balance your helicopter and it great reduces the chance of breaking the rotor blade or any expensive parts from hitting any obstacle