This is a Two-Speed 43 Tooth Spur Gear for the HPI Nitro RS4 3.
This is one of the two main gears on a Nitro RS4 3 equipped with a 2-speed.
Black nylon construction
One 43T spur gear
The remainder of the two-speed transmission
Outer diameter: 45mm (1.78")
Inner diameter: 14mm (0.56")
Thickness: 5.2mm (0.21")