This is the 5mm Bore 11T Hardened Steel Pinion Gear from Novak.

FEATURES
Compatible with Novak Ballistic 550, 4PHD 4-Pole, HD8 1/8 and other
1/8 scale, 550-size and 4-pole brushless motors
with 5mm output shaft
Ultimate pinion gear for 1/8th Electric, 4X4 SCT, Monster Trucks, and
other heavy-duty and go-fast applications
Engineered for maximum durability
Hardened steel construction for incredible strength and resistance to
corrosion
CNC-machined for ultra-precise concentricity
For use with 5mm shaft motors
Stamped for easy identification
Also available in cost-saving 3-pack sets

INCLUDES
5mm Mod.1 11T Hardened Steel Pinion Gear with 4x4mm Set Screw

REQUIREMENTS
Installation on the motor and tightening set screw

SPECIFICATIONS
Length: 12mm
Number of Teeth: 11
Gear Pitch: Mod 1
Mounting Hole Diameter: 5mm