shot-in Heavy Duty 21T Metal Servo Horn arm 12G-17G CS DS-929MG 939MG 919MG S MaterialCNC Aluminium ColourSilver 21T 21Tooth Be suitable for 12G-18G metal gear servo (just like MG90 MG90S CS-929MG CS-939MG DS-929MG DS-939MG DS-919MG MD922 MD933 Etc..) the 3 hole separation distance is 2MM,the length is 24mm.