These are the Tail Drive Shaft Bevel Gear Ball Bearings for the Thunder Tiger Raptor 60 and Raptor 90 Helicopters. FEATURES: Steel construction Silver in color INCLUDES: Two 12x18x4mm ball bearings REQUIRES: Installation into tail drive shaft SPECS: Inner Diameter: 12mm Outer Diameter: 18mm Thickness: 4mm Thunder TigerPart TTRPV0197