This 12JS200T-1707030 auxiliary box drive gear is for FAST 12JS200T Fuller type 12-speed heavy-duty transmission. Installed inside the gearbox splitter auxiliary box, it transfers torque for high/low range gear switching. Made of forged alloy steel with precision grinding and shot peening strengthening treatment. It delivers high hardness, outstanding wear resistance and strong heavy-torque bearing capacity. Suitable for long-distance heavy haul, frequent high-low shifting and mountain complex road conditions. Every gear passes dimension, runout, hardness and tooth profile inspection before factory shipment. Fixes common failures such as tooth chipping, abnormal noise and power interruption of auxiliary box. Essential OEM replacement spare part for 12JS200T transmission auxiliary box overhaul.