TKR8151 Differential Ring Gear (CNC, 40t, use with TKR8152)These gears are CNC machined from high quality steel, then hardened for durability. They will provide smoother and more efficient operation than our standard gears. They also run quieter than the standard gears. The ring and pinion should be run as a set (TKR8151 and TKR8152) and should not be mixed with any other gear sets. True straight cut design for maximum efficiencySmoother and quieter than our standard gearsCNC hardened steel construction