This is the optional Team Durango 50T Mod 1 Steel Spur Gear.

For the Team Durango DESC10 Short Course Truck, DEX8 Buggy and the
DEX8T Truggy
Hardened steel construction
Replaces TD310586 stock plastic 50T spur gear
Number of teeth stamped on gear for easy identification

50T Mod 1 Steel Spur Gear