These are Ball Bearings used on the Thunder Tiger Raptor 30, Raptor 60 and Raptor 90 Helicopters. FEATURES: Steel construction Silver in color INCLUDES: Four 5x10x4mm ball bearings REQUIRES: Installation on to helicopter SPECS: Inner Diameter: 5mm Outer Diameter: 10mm Thickness: 4mm lmm 10.11.10 ir/jxs