This is a 17T 5mm Pinion Gear from Ofna. FEATURES: Steel construction Fits 5mm motor shafts INCLUDES: One 17T Pinion Gear One 4x4mm Set Screw REQUIRES: Installation SPECS: Thickness: 14mm (0.55") Inner Diameter: 5mm (0.20") cnh 4/13/10 ir/jxs