This is the 11T Pinion Gear for the Thunder Tiger E550 and E620 Helicopters. FEATURES: Steel construction Black in color Replaces worn or damaged pinion gears INCLUDES: One 11T pinion gear REQUIRES: Installation onto helicopter SPECS: Length: 22mm (0.87") Inner Diameter: 5mm (0.20") Teeth: 11 lgm 03/09/11 ir/jxs