This is the optional Mod 1 21 Tooth Pinion Gear for the Team Durango DESC410v2 Pro Spec 4WD Short Course Truck, TDRC0140. FEATURES: Aluminum construction For 550 4-pole motor usage Number of teeth stamped on gear INCLUDES: Mod 1 21 Tooth Pinion Gear with Set Screw jxs 09/14/12 ir/jxs